Integrated hydrocarbon reforming system and controls

ABSTRACT

A hydrocarbon reformer system including a first reactor configured to generate hydrogen-rich reformate by carrying out at least one of a non-catalytic thermal partial oxidation, a catalytic partial oxidation, a steam reforming, and any combinations thereof, a second reactor in fluid communication with the first reactor to receive the hydrogen-rich reformate, and having a catalyst for promoting a water gas shift reaction in the hydrogen-rich reformate, and a heat exchanger having a first mass of two-phase water therein and configured to exchange heat between the two-phase water and the hydrogen-rich reformate in the second reactor, the heat exchanger being in fluid communication with the first reactor so as to supply steam to the first reactor as a reactant is disclosed. The disclosed reformer includes an auxiliary reactor configured to generate heated water/steam and being in fluid communication with the heat exchanger of the second reactor to supply the heated water/steam to the heat exchanger.

RELATED REFERENCES

The present invention claims priority of U.S. Provisional PatentApplication Nos. 60/132,184 and 60/132,259, both filed on May 3, 1999.

GOVERNMENT RIGHTS

The United States Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofDE-FC02-97EE50472 awarded by the Department of Energy (DOE).

TECHNICAL FIELD

The present invention is generally related to an integrated hydrocarbonfuel reforming system for reforming a gaseous or liquid hydrocarbon fuelto produce a hydrogen-rich product stream used in, among other things,hydrogen fuel cells. More particularly, the invention is directed to animproved integrated hydrocarbon reforming system, including, anautothermal reformer having distinct zones for partial oxidationreforming and steam reforming, and also having an integrated shift bedfor reducing carbon monoxide in the product stream, a preferentialoxidation reactor, and an auxiliary reactor.

BACKGROUND OF THE INVENTION

Reforming of hydrocarbon fuels to make hydrogen is well known in theart. Conventionally, hydrocarbons are reformed predominately inlarge-scale industrial facilities providing hydrogen for bulk storageand redistribution, or producing hydrogen as an on-line, upstreamreagent for another large-scale chemical process. For the most part,these prior processes operate continuously and at steady-stateconditions.

More recently, however, a strong interest has developed in providinghydrocarbon-reforming reactors integrated with an end use of thehydrogen. Also, there is a strong interest to develop a low-cost,small-scale source for hydrogen that can replace the need for storinghydrogen gas on site or on board. More particularly, a great interesthas developed in providing reactors for producing hydrogen, which can beintegrated with a fuel cell which uses hydrogen as a fuel source togenerate electricity. Such hydrogen generator/fuel cell systems arebeing pursued for stationary uses such as providing electrical power toa stationary facility (home or business), for portable electric poweruses, and for transportation.

The use of fuel cells, such as polymer electrolyte membrane fuel cells(PEM-FC), has been proposed for many applications, specificallyincluding electrical vehicular power plants used to replace internalcombustion engines. Electrochemical fuel cells convert fuel and oxidantto electricity and reaction product. Hydrogen is most commonly used asthe fuel and is supplied to the fuel cell's anode. Oxygen (commonly asair) is the cell's oxidant and is supplied to the cell's cathode. Thereaction product is water.

Efficiency and low emissions are two benefits of fuel cell systems. Asystem running near 40% efficiency will offer the opportunity tosignificantly reduce fuel consumption and CO₂ production compared toconventional gasoline internal combustion engines. Perhaps moreimportantly, it has been shown that fuel cell systems, even when runningwith an onboard fuel processor, offer an opportunity to greatly reduceemissions of NOx, carbon monoxide, and hydrocarbons in automotiveapplications.

There are many technical requirements for reactors used in suchapplications, which are not required of traditional large or small-scalehydrogen generating reactors. For example, it is of particular interestto have such a system where the fuel cell can provide “power on demand.”Hence, hydrogen must be produced at required variable levels on demand.In other words, the hydrogen producing reactors must be sufficientlydynamic to follow the load. It is also of interest that such systemsperform well upon start-up and shutdown cycling. In particular, it isdesirable to have these integrated systems be stable through repeatedon-off cycling including being ready to come back on-line in arelatively short time.

Another marked difference between proposed integrated systems andtraditional reactors is that there must be sufficient processing in theintegrated system itself, of the hydrocarbon feed stock so as to notonly give a yield of hydrogen sufficient to meet the demand, but also tominimize byproducts of reaction including contaminants. In large-scalereactor systems, which produce enormous volumes and run continuously;space, weight, and cost of auxiliary systems is not so critical as inthe integrated, smaller-scale reformers, especially those proposed forportable power or transportation applications. For example, carbonmonoxide may be considered an undesirable reaction product on board afuel cell powered automobile. However, in a steady state conventionalprocess, the carbon monoxide can easily be handled by auxiliaryseparation systems, and may in fact be welcomed for its use in asynthesis gas to make acetic acid, dimethyl ether, and alcohols.

In short, the challenge for the smaller-scale, dynamic, integratedprocessors is the idea that what goes in the reformer, must come out atthe same end as the desired hydrogen gas. Accordingly, processing has tobe more complete and efficient, while it must also be cost effective,lightweight, and durable. The processing must be sufficient to reduce oreliminate species in the product gas which are harmful to the end use(for example, fuel cells) or other down stream components.

Another challenge exists for the proposed integrated systems withrespect to the hydrocarbon feed stock. To be of maximum benefit, theproposed integrated systems should be able to use existinginfrastructure fuels such as gasoline or diesel fuels. These fuels werenot designed as a feed stock for generating hydrogen. Because of this,integrated systems are challenged to be able to handle the wide varietyof hydrocarbons in the feed stock. For example, certain reformingbyproducts such as olefins, benzene, methyl amide, and higher molecularweight aromatics can cause harm to catalysts used in reforming orpurifying steps and may harm the fuel cell itself. Impurities in thesefuels such as sulfur and chlorine can also be harmful to reactorcatalysts and to the fuel cell.

It is also important to note, that a natural byproduct of hydrocarbonreforming is carbon monoxide. Carbon monoxide can poison proton exchangemembrane fuel cells, even at very low concentrations of, for example,less than 100 ppm. Typical carbon monoxide levels exiting a fuelprocessing assembly (“FPA”) are about 2,000 to 5,000 ppm. This poses aproblem for an integrated reactor system that is not faced bytraditional reforming processes where significant carbon monoxideconcentrations are either a useful co-product, or can be separated fromthe product gas without undue burden on the system economics as a whole.

Also, as noted above, integrated systems proposed to date are expectedto transfer the total of the reformate to a fuel cell. Accordingly,techniques which separate carbon monoxide from hydrogen, such aspressure swing adsorption (“PSA”) or hydrogen permeable membraneseparation, have the deficit of having to provide an alternate means fordisposal or storage of the carbon monoxide. Both of the aforementionedtechniques also suffer in efficiency as neither converts the carbonmonoxide (in the presence of water) to maximize hydrogen production. PSAalso suffers from high cost and space requirements, and presents alikely unacceptable parasitic power burden for portable power ortransportation applications. At the same time, hydrogen permeablemembranes are expensive, sensitive to fouling from impurities in thereformate, and reduce the total volume of hydrogen in the reformatestream.

One known method of reforming gaseous or liquid hydrocarbon fuels is bycatalytic steam reforming. In this process a mixture of steam and thehydrocarbon fuel is exposed to a suitable catalyst at a hightemperature. The catalyst used is typically nickel and the temperatureis usually between about 700° C. and about 1000° C. In the case ofmethane, or natural gas, hydrogen is liberated in a catalytic steamreforming process according to the following overall reaction:

CH₄+H₂O→CO+3H₂  (1)

This reaction is highly endothermic and requires an external source ofheat and a source for steam. Commercial steam reformers typicallycomprise externally heated, catalyst filled tubes and rarely havethermal efficiencies greater than about 60%.

Another conventional method of reforming a gaseous or liquid hydrocarbonfuel is partial oxidation (POx) reforming. In these processes a mixtureof the hydrocarbon fuel and an oxygen containing gas are broughttogether within a POx chamber and subjected to an elevated temperature,preferably in the presence of a catalyst. The catalyst used is normallya noble metal or nickel and the high temperature is normally betweenabout 700° C. and about 1200° C. for catalyzed reactions, and about1200° C. to about 1700° C. for non-catalyzed reactions. In the case ofmethane, or natural gas, hydrogen is liberated in a POx chamberaccording to the following overall reaction:

CH₄+½O₂→CO+2H₂  (2)

This reaction is highly exothermic and once started generates sufficientheat to be self sustaining. That is, no external heat supply or steamsupply is required. The catalytic partial oxidation reforming techniqueis simpler than the catalytic steam reforming technique, but is not asthermally efficient as catalytic steam reforming.

An additional known method of reforming a hydrocarbon fuel is byautothermal reforming, or “ATR”. An autothermal reformer uses acombination of steam reforming and partial oxidation reforming. Wasteheat from the partial oxidation reforming reaction is used to heat thethermally steam reforming reaction. An autothermal reformer may in manycases be more efficient than either a catalytic steam reformer or acatalytic partial oxidation reformer. Again, using methane, or naturalgas, as the hydrocarbon fuel, hydrogen is liberated according to thefollowing overall reaction:

CH₄+yH₂O+(1−y/2)O₂→CO₂+(2+y)H₂, where 0<y<2  (3)

Consideration of the standard enthalpies of formation shows thatautothermal operation is theoretically achieved when y=1.115.

In addition to the reforming reactions discussed above it is usuallynecessary to consider the effects of another reaction occurring, the socalled “water gas shift reaction.” Because the equilibrium of thisreversible reaction is temperature (T) dependent, and at hightemperatures carbon monoxide and water tend to be produced, the effectswarrant consideration. In the water gas shift reaction the followingoverall reaction occurs:

CO+H₂O_((g))⇄CO₂+H₂  (4)

More favorably, however, is that given equilibrium conversion at lowtemperatures carbon dioxide and hydrogen tend to be produced.

Typical reformers produce carbon dioxide and hydrogen, and consequentlysome carbon dioxide and hydrogen react to produce concentrations ofcarbon monoxide and water due to the reverse water gas shift reactionoccurring in the reforming chamber. As mentioned previously, this isundesirable because the concentration of carbon monoxide must be eithercompletely removed or at least reduced to a low concentration—i.e., lessthan about 100 ppm after the shift reaction—to avoid poisoning the anodeof the PEM-FC. Carbon monoxide concentrations of more than 20 ppmreaching the PEM-FC can quickly poison the catalyst of the fuel cell'sanode. In a shift reactor, water (i.e., steam) is added to thehydrocarbon reformate/effluent exiting the reformer, in the presence ofa suitable catalyst, to lower its temperature, and increase the steam tocarbon ratio therein. The higher steam to carbon ratio serves to lowerthe carbon monoxide content of the reformate to less than 100 ppmaccording to the shift reaction (4) above. Ideally, the carbon monoxideconcentration can be maintained below 1 ppm with the right shiftcatalyst, but the temperature required for this, about 100° C.-125° C.,is too low for operation of current shift catalysts.

Advantageously, it is possible to recover some hydrogen at the same timeby passing the product gases leaving the reformer, after cooling, into ashift reactor where a suitable catalyst promotes the carbon monoxide andwater/steam to react to produce carbon dioxide and hydrogen. The shiftreactor provides a convenient method of reducing the carbon monoxideconcentration of the reformer product gases, while simultaneouslyimproving the yield of hydrogen.

However, some carbon monoxide still survives the shift reaction.Depending upon such factors as reformate flow rate and steam injectionrate, the carbon monoxide content of the gas exiting the shift reactorcan be as low as 0.5 mol percent. Any residual hydrocarbon fuel iseasily converted to carbon dioxide and hydrogen in the shift reactor.Hence, shift reactor effluent comprises not only hydrogen and carbondioxide, but also water and some carbon monoxide.

The shift reaction is typically not enough to sufficiently reduce thecarbon monoxide content of the reformate (i.e., below about 100 ppm).Therefore, it is necessary to further remove carbon monoxide from thehydrogen-rich reformate stream exiting the shift reactor, prior tosupplying it to the fuel cell. It is known to further reduce the carbonmonoxide content of hydrogen-rich reformate exiting a shift reactor by aso-called preferential oxidation (“PrOx”) reaction (also known as“selective oxidation”) effected in a suitable PrOx reactor. A PrOxreactor usually comprises a catalyst bed which promotes the preferentialoxidation of carbon monoxide to carbon dioxide by air in the presence ofthe diatomic hydrogen, but without oxidizing substantial quantities ofthe H₂ itself. The preferential oxidation reaction is as follows:

CO+½O₂→CO₂  (5)

Desirably, the O₂ required for the PrOx reaction will be no more thanabout two times the stoichiometric amount required to react the CO inthe reformate. If the amount of O₂ exceeds about two times thestoichiometric amount needed, excessive consumption of H₂ results. Onthe other hand, if the amount of O₂ is substantially less than about twotimes the stoichiometric amount needed, insufficient CO oxidation willoccur. The PrOx process is described in a paper entitled “PreferentialOxidation of CO over Pt/γ-Al₂O₃ and Au/α-Fe₂O₃: Reactor DesignCalculations and Experimental Results” by M. J. Kahlich, et al.published in the Journal of New Materials for Electrochemical Systems,1988 (pp. 39-46), and in U.S. Pat. No. 5,316,747 to Pow et al.

PrOx reactions may be either (1) adiabatic (i.e., where the temperatureof the reformate (syngas) and the catalyst are allowed to rise duringoxidation of the CO), or (2) isothermal (i.e., where the temperature ofthe reformate (syngas) and the catalyst are maintained substantiallyconstant during oxidation of the CO). The adiabatic PrOx process istypically effected via a number of sequential stages which progressivelyreduce the CO content. Temperature control is important in both systems,because if the temperature rises too much, methanation, hydrogenoxidation, or a reverse shift reaction can occur. This reverse shiftreaction produces more undesirable CO, while methanation and hydrogenoxidation negatively impact system efficiencies.

In either case, a controlled amount of O₂ (e.g., as air) is mixed withthe reformate exiting the shift reactor, and the mixture is passedthrough a suitable catalyst bed known to those skilled in the art. Tocontrol the air input, the CO concentration in the gas exiting the shiftreactor is measured, and based thereon, the O₂ concentration needed forthe PrOx reaction is adjusted. However, effective real time CO sensorsare not available and accordingly system response to CO concentrationmeasurements is slow.

For the PrOx process to be most efficient in a dynamic system (i.e.,where the flow rate and CO content of the hydrogen-rich reformate varycontinuously in response to variations in the power demands on the fuelcell system), the amount of O₂ (e.g., as air) supplied to the PrOxreactor must also vary on a real time basis in order to continuouslymaintain the desired oxygen-to-carbon monoxide concentration ratio forreaction (5) above.

Another challenge for dynamic operation is that the reformate atstart-up contains too much carbon monoxide for conversion in the PrOxreactor and, therefore, is not suitable for use in a PEM-FC. Oneapproach to this problem is to discharge this unsuitable reformatewithout benefit, and potentially to the detriment of the environment.The partially reformed material may contain unacceptable levels ofhydrocarbons, carbon monoxide, sulfur, noxious oxides, and the like. Itwould be an advantage to provide a process which utilizes the wastereformate to assist in the preheating of unreformed fuel before itsentry into the reforming chamber, while simultaneously converting theharmful constituents of the waste reformate to acceptable emissions.

A PEM-FC typically does not make use of 100% of the incoming hydrogenfrom the reformer/reactor. Therefore, anode gases—mostly unusedhydrogen—are discharged from the fuel cell simultaneous with the inputof hydrogen. It would be an advantage in the industry to make use ofthis combustible material to assist the preheating of unreformedhydrocarbon fuel or for steam generation. Systems already proposedemploy so called “tail gas combusters” to burn off such fuel cellexhaust gases.

The present invention addresses the above problems and challenges andprovides other advantages as will be understood by those in the art inview of the following specification and claims.

SUMMARY OF THE INVENTION

In one embodiment of the present invention a hydrocarbon reformer systemcomprising a first reactor configured to generate hydrogen-richreformate by carrying out at least one of a non-catalytic thermalpartial oxidation, a catalytic partial oxidation, a steam reforming, andany combinations thereof, a second reactor in fluid communication withthe first reactor to receive the hydrogen-rich reformate, and having acatalyst for promoting a water gas shift reaction in the hydrogen-richreformate, and a heat exchanger having a first mass of two-phase watertherein and configured to exchange heat between the two-phase water andthe hydrogen-rich reformate in the second reactor, the heat exchangerbeing in fluid communication with the first reactor so as to supplysteam to the first reactor as a reactant is disclosed. It is an aspectof the present embodiment wherein a preferred ratio of the mass ofcatalyst to the first mass of the two-phase water is greater than 1.

It is also an aspect of the reformer to provide a preferred ratio of thefirst mass of two-phase water to catalyst greater than 3. Still anotheraspect of the invention provides wherein the ratio of the first mass oftwo-phase water to catalyst is greater than 5.

It is another aspect of the present embodiment to provide the disclosedreformer including an auxiliary reactor configured to generate heatedwater/steam and being in fluid communication with the heat exchanger ofthe second reactor to supply the heated water/steam to the heatexchanger.

In a method for controlling a hydrocarbon reformer during dynamic loadoperation, the present invention discloses the steps of supplying ahydrocarbon fuel at a first to a reactor which generates a hydrogen-richreformate, generating steam under a desired pressure in a loop whichincludes a steam generator and a water/steam separator, supplying thesteam at a first rate to the reactor, maintaining a substantially stablesteam pressure in the loop at the first rate of supplying steam andhydrocarbon fuel, in response to a change in demand for hydrogen-richreformate from the generator, changing the rate of supply of each of thehydrocarbon fuel and the steam to second supply rates respectively,permitting the pressure of the loop to change in pressure in response tothe second rate of supply within an acceptable range for period of time,and generating enough steam to return the loop steam pressure to thedesired pressure.

It is one aspect of the disclosed method to provide the acceptable rangewithin which the steam pressure is permitted to change to be about 200psi, but more preferably 150 psi.

In still another method of the present invention a hydrocarbon reformeris controlled by the steps of providing a first mass of catalyst in afirst reactor zone for promoting a water gas shift reaction in ahydrogen-rich reformate, generating steam in an auxiliary reactor, andtransferring heat from the steam to the first mass of catalyst.

In a hydrocarbon reformer system the present invention discloses a firstreactor configured to generate hydrogen-rich reformate by carrying out areforming reaction, the reaction selected from the group of reactionscomprising: thermal (or gas-phase) partial oxidation; catalytic partialoxidation; steam reforming; and combinations thereof, a second reactorin fluid communication with the first reactor to receive thehydrogen-rich reformate, and having a catalyst for promoting a water gasshift reaction in the hydrogen-rich reformate, and at least one heatexchanger having a first mass of two-phase water therein and configuredto exchange heat between the two-phase water and the hydrogen-richreformate in the second reactor, the heat exchanger being in fluidcommunication with the first reactor so as to supply steam to the firstreactor as a reactant. The disclosed invention provides wherein a ratioof the mass of catalyst to the first mass of the two-phase water isgreater than 1, or optionally greater than 3, or optionally greater than5.

It is also an aspect of the present embodiment to provide a hydrocarbonreformer including an auxiliary reactor configured to generate heatedwater/steam and being in fluid communication with the heat exchanger ofthe second reactor to supply the heated water/steam to the heatexchanger.

These and other aspects of the present invention set forth in theappended claims may be realized in accordance with the followingdisclosure with particular reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions of the present invention are discussed withparticular reference to the appended drawings of which:

FIG. 1 is a schematic view of one embodiment of a system of the presentinvention showing the relationship of selected sub-systems to oneanother;

FIG. 2 is a schematic view of another embodiment of the system of thepresent invention showing fluid transport and flow between sub-systems;

FIG. 3 is a side view of one embodiment of a reformer reactor subsystemof the present invention;

FIG. 4 is an exploded view of a pressure vessel shell of the reformerreactor of FIG. 3;

FIG. 5 is an exploded view of an inner protective shell of the reformerreactor of FIG. 3;

FIG. 6 is a side cross-sectional view of the reformer reactor shown inFIG. 3;

FIG. 7 is an exploded view of an autothermal reforming vessel of thereformer reactor shown in FIG. 6;

FIG. 8 is an exploded view of a POx chamber of the reformer shown inFIG. 6;

FIG. 9 is a top view of a steam ring of the reformer shown in FIG. 6;

FIG. 10 is a top cross-sectional view of an air inlet section of the POxchamber shown in FIG. 8;

FIG. 11 is a cross-sectional view of a pre-mixing manifold shown in FIG.6;

FIG. 12 is a side view of one embodiment of the PrOx reactor of thepresent invention;

FIG. 13 is a side cross-sectional view of the PrOx reactor shown in FIG.12;

FIG. 14 is a top cross-sectional view of the PrOx reactor shown in FIG.12;

FIG. 15 is a diagrammatic illustration of a two stage PrOx reactorembodiment of the present invention;

FIG. 16 is a side view of one embodiment of a second stage PrOx reactor,as shown in FIG. 15;

FIG. 17 is a side cross-sectional view of the embodiment of the secondstage PrOx reactor shown in FIG. 16;

FIG. 18 is a diagrammatic illustration of an alternative PrOx reactorsystem design having a two catalyst beds configured in parallel;

FIG. 19 is a diagrammatic illustration of a two-stage PrOx arrangementhaving a chiller condenser in line;

FIG. 20 is a side cross-sectional view of one embodiment of an auxiliaryreactor of the present invention;

FIG. 21 is a side cross-sectional view of an alternative embodiment ofan auxiliary reactor of the present invention;

FIG. 22 is a side cross-sectional view of another alternative embodimentof an auxiliary reactor of the present invention;

FIG. 23 is a diagrammatic illustration of a water/steam loop andwater/steam controls of the present invention;

FIG. 24 is a diagrammatic illustration of one embodiment of the presentinvention showing operational control points;

FIG. 25 is a diagrammatic illustration of a reformate flow through asystem according to the present invention;

FIG. 26 is a diagrammatic illustration of a sample start-up procedurefor the reformer, PrOx and auxiliary reactors of the system of FIG. 2;

FIG. 27 is a diagrammatic illustration of a sample steady-stateoperation for the fuel cell system of the present invention; and

FIG. 28 is a diagrammatic illustration of control points for a reformer,an auxiliary reactor, and a steam separator in one embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

While the present invention is susceptible of embodiment in manydifferent forms, this disclosure will described in detail, preferredembodiments of the invention with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the broad aspect of theinvention to the embodiments discussed or illustrated.

I. System and Sub-System Structure

Referring generally to the appended FIGS. 1-28, the hydrocarbonreforming process and apparatus of the present invention can be morereadily understood. The disclosed hydrocarbon reforming systemarchitecture is generally referenced by the number “10” in the followingdisclosure and drawings. Other specific components, such as thereforming chambers, catalyst beds, auxiliary reactors (e.g., PrOxreactors, tail gas combusters, etc.), and their respective parts, aresimilarly and consistently numbered throughout this disclosure. Whilethe present hydrocarbon reforming system 10 is disclosed in combinationwith a PEM-fuel cell, such as those used for transportation systems andthe like, the systems and components according to the invention may beemployed in other applications calling for a supply of hydrogen-richsyngas. More particularly, the disclosed systems and subcomponentsthereof will be preferred in applications where size, weight,portability, and energy efficiencies are desired Examples of such usesinclude portable power units, transportation, on demand merchanthydrogen, and small power plant (e.g., household backup or primary powersystems).

As shown in FIG. 1, the integrated hydrocarbon reforming system 10(“system,” “reforming system,” and like variations) is comprised of areformer reactor 12, a preferential oxidation reactor 13 (PrOx), anauxiliary reactor 14, an associated fuel cell 15, and a network of fluidtransport structure 16. In general, the reformer reactor 12 isdownstream of the auxiliary reactor 14 and is in fluid communicationtherewith via fuel line 17 . The reformer reactor 12 is in turn upstreamof the PrOx reactor 13 and is in fluid communication therewith viaconduit 20.

In this embodiment, the auxiliary reactor 14 can be used with liquidhydrocarbon fuels to preheat, desulfurize, and/or to vaporize the fuelbefore transfer through conduit 20 to the reformer reactor 12. Thispreheating may be used only for a temporary period such as duringreformer start-up, as exemplified in FIG. 2. In that embodiment, thefuel preheat/vaporization task (and the hydrocarbon fuel source) istransferred to heat exchangers within a shift catalyst bed in thereformer 12 after the shift bed has risen to a desired temperature afterstart-up. The auxiliary reactor 14 can also be used to desulfurizeliquid hydrocarbon feed stocks. In a preferred method, thedesulfurization is carried out catalytically. The hydrocarbon fuel istransported from a hydrocarbon fuel source 18 to the auxiliary reactor14 via fuel line 9. The auxiliary reactor 14 may also be used to heat orpreheat water to make steam used in the reformer 12 as a reactant and/ora heat transfer medium. The auxiliary reactor 14 can also be used toreact excess hydrogen and other gases exhausted from the anode of thefuel cell 15. Any heat from this reaction may be synergistically used inthe aforementioned preheating or desulfurization processes. Theauxiliary reactor 14 may also be used to combust reformate from thereformer 12 as desired. For example, upon start up or othercircumstances when the reformate may not be of desired quality totransfer to the PrOx reactor 12 or the fuel cell 15, then it can beoptionally routed to the auxiliary reactor 14 via a valve 28 in conduit26. Again, any heat from this reaction may be synergistically used inthe aforementioned preheating or desulfurization processes. Details ofvarious embodiments of auxiliary reactor 14 are disclosed in detailbelow. With each embodiment, a preferred fuel or system support functionis disclosed.

In the system 10, water is first introduced from a reservoir to theauxiliary reactor 14. Depending on the desired heating, the water istransferred as heated water, steam or two phase water-steam. Of coursethe level of heating is a matter of particular design relative to theparticular system goals as exemplified by the preferred embodimentsbelow. The water/steam/steam-water is synergistically transferred to thereformer 12. Depending on system goals and design, thewater/steam/water-steam can be routed through heat exchangers in shiftcatalyst beds (see for example, FIG. 6 and reformer 12 with heatexchange or boiler tubes 39 embedded in a low temperature shift catalystbed (“LTS”) 36). The water/steam/water-steam may also be then directedto heat exchangers in the PrOx reactor 13 for additional heat exchangewith reformate during the exothermic reactions proceeding therein.

In alternate embodiments, an alternate source of vaporized fuel may alsobe supplied to the reformer 12 directly by such as supply line 19disclosed in FIG. 2. In this embodiment, the auxiliary reactor 14 isused to provide vaporized fuel to the reformer 12 during start-up. Uponreaching a desired temperature in a high temperature shift bed (“HTS”)37, hydrocarbon feed stock is then fed directly into heat exchangers 39in the HTS 37 to preheat/vaporize the fuel before reaction. The fuelsupply from the auxiliary reactor 14 can then be terminated.

Air is supplied to the system 10 at various points at the fuel inlet tothe HTS bed 37, the conduit between the LTS bed 36, and the PrOx reactor13. Greater detail on these operations are found later in thisspecification (see section below, System and Sub-System Control andOperation). The reformate flow is illustrated separately in FIG. 26.

A. Reformer Reactor:

One reformer 12 preferred for the present system 10 (FIG. 1) isdisclosed in FIGS. 3-11. In overview, in accordance with aspects of theinvention, an autothermal fuel reformer is uniquely spatially andthermally integrated. Also, the autothermal reformer is housed andintegrated spatially and thermally with water-gas shift reactors. Alsospatially and thermally integrated into the reformer 12 are unique heatexchangers 39 for preheating air and fuel, generation of steam, andactive cooling of various reaction zones. Advantageously, steamgenerated in shift catalyst beds of reformer 12 provide arapidly-deliverable supply of steam for combustion upon increased demandon the system 10.

The reformer 12 shown in FIGS. 4 and 5, is generally comprised of apressure containing cylinder 21, thermal insulation rings 29, 29′, andan inner protective sleeve 30. As disclosed in FIG. 6, these componentsare coaxially nested and closed at axially opposed ends, 22 and 23, ofcylinder 21 by end plates 26 and 28, respectively. As such, the cylinder21 provides pressure containment, the insulation rings 29, 29′ isolatethe cylinder 24 from reaction temperatures, and the sleeve 30 preventserosion or contamination of the insulating rings 29, 29′.

The outer cylinder 24 has a peripheral flange 25 along its lowerperipheral edge, and is preferably manufactured from a high gradestainless steel, or an equally strong and flexible metal or alloy. It isdesirable that the cylinder 24 be capable of withstanding internalpressures (e.g., one preferred method of operation maintains reformerpressures at about three atmospheres). The top plate 26 sits within aseat 27 defined in a circumferential top edge of the cylinder 24. This,with suitable gasketing forms a seal at one end of the reformer 12.

FIG. 5 discloses that the inner protective sleeve 30 preferably includesan integral flange 32. As disclosed in FIG. 6, the flange 32 is sized tohave a diameter sufficient to under lap flange 25 of the outer cylinder24. Bottom plate 28 attaches to the opposite axial end of the cylinder24. The flange 32 passes beneath the insulation sleeves 30 to thepressure cylinder 24 where it is sandwiched between the outer cylinderflange 25 and the bottom plate 28. Several bolts are used to secure thethree layers tightly together. Gasketing material may also be utilizedto effect or assist sealing. This provides a secure seal againstreformate infiltrating into the space between the sleeve 30 and thecylinder 24 and maintains the integrity of the thermal insulation 29.

The protective sleeve 30, as employed with reformer 12, has two sectionsof different diameters. As disclosed in FIGS. 5 and 6, a top portion ofthe protective sleeve 30 has a larger diameter than the bottom portion.The purpose of this smaller diameter portion is to provide a greaterspace between the inner protective sleeve 30 and the pressure containingcylinder 21 so that additional insulation 29 can be accommodatedadjacent the HTS bed 37 of the reformer 12.

The bottom flange 32, is preferably configured to extend radiallyoutwardly (FIG. 5), but may be configured to extend radially inwardly(not shown). A suitable seal may also be formed by a channel (not shown)defined in the plate 26. The flange 32 of sleeve 30 preferably forms acomplete ring about the protective shell (FIG. 5), but may bediscontinuous for some applications (not shown). The purpose is toprovide a structurally sound connection and a seal against fluid flow.

The thermal insulation rings 29, 29′ facilitate retention of heat withinthe reformer 12 during operation. The rings 29, 29′ may be comprised ofany suitable insulative material known to those skilled in the art, andmay be provided in a preformed shape as disclosed in FIG. 5, such as afoam, rolled sheet. However, pellets or granules, fiber blanket, orother desired form may be suitable.

All of the necessary inlets and outlets each of which will be discussedbelow—are provided for within the top plate 26 and bottom plate 28, asshown in FIGS. 3-6.

Located within the inner protective sleeve 30 of reformer reactor 12 (asdisclosed in FIG. 6), are structures to provided four distinct reactionzones or chambers: a partial oxidation (“POx”) zone or chamber 34, asteam reforming zone 35, a low temperature shift (LTS) bed or zone 36(filled with catalyst), and a high temperature shift (HTS) bed or zone37 (filled with catalyst). A helical preheat tube 38 for steam/fuel, ahelical water/steam tube 39, and a helical oxygen/air tube 40 aredisposed within the LTS and HTS beds, 36 and 37, respectively. A fuelinlet 41 on plate 28 is provided to communicate with fuel conduit 19,for transferring heated fuel from the auxiliary reactor 14 to thehelical fuel tube 38. An inlet 42 disposed in the bottom plate 28 of thereformer reactor 12 delivers a supply of oxygen-containing gas to thehelical oxygen/air tube 40 from an oxygen gas source 43. A water/steamline 44 delivers a supply of two-phase water to water inlet 45, which inturn transfers the fluid to the water/steam helical tube 39. Finally,disposed in the top plate 26 of the reformer reactor 12 is a reformateoutlet 31 which discharges the reformate through a reformate conduit 20,preferably into a preferential oxidation reactor 13, as illustrated byFIG. 25.

The POx chamber 34 and steam reforming zone 35 together define anautothermal reforming vessel 46. The autothermal reforming vessel 46 isshown in an exploded view in FIG. 7. The outermost bounds of theautothermal reforming vessel 46 are defined by a second closedcylindrical chamber 47 having a sidewall 51 closed at its axial top endby a top plate 52 welded thereon. The sidewall 51 of the secondcylindrical chamber 47 is preferably skirted, as shown in FIG. 7. Asecond insulation layer 48 surrounds the autothermal reforming vessel 46and may be made of any conventional insulative material known to thoseskilled in the art.

A third cylindrical wall 49 is provided around the second insulationlayer 48. The third cylindrical wall 43 is closed at its upper axial endby a top plate 50. Several bolt cylinders 53 are attached to the topplate 50 to permit attachment to the top plate 26 of the pressure vesselshell 24.

The POx chamber 34 of the autothermal reforming vessel 46 may be chargedwith a catalyst and operated to perform catalytic POx reactions. It ispreferably operated without a catalyst to conduct gas-phase flame-typepartial oxidation reactions. Referring back to FIG. 6, it can be seenthat the POx chamber 34 is also generally defined by a cylindrical tube54 which acts to separate the two reforming zones while providingradiant heat transfer from the POx chamber 34 to the steam reformingzone 35 through the metal walls of cylinder tube 54. The cylindricaltube 54 has a central axis preferably coincident with the longitudinalaxis (x) of the reformer reactor 12.

Referring to FIG. 8, the POx chamber 34 is seen in exploded view asthree annular sections: a base section 55, an inlet section 56, and thecylindrical tube 54. The tube 54 has a first end 57 where preheated fuelmixture enters via an inlet 58 disposed within the inlet section 56, anda closed ventilated end 59 having a plurality of apertures 60 to allowthe partially reformed gas to flow radially into a the first end of thesteam reforming zone 35.

The steam reforming zone 35 is also cylindrical and disposed annularlyabout the POx chamber 34 and extending substantially the entire lengthof the POx chamber 34. The steam reforming zone 35 in the presentembodiment is packed with a nickel containing catalyst, but may includecobalt, platinum, palladium, rhodium, ruthenium, iridium, and a supportsuch as magnesia, magnesium aluminate, alumina, silica, zirconia, singlyor in combination. Alternatively, the steam reforming catalyst can be asingle metal, such as nickel, or a noble metal supported on a refractorycarrier like magnesia, magnesium aluminate, alumina, silica, orzirconia, singly or in combination, promoted by an alkali metal likepotassium. At a second end of the steam reforming zone 35, where thereformate stream is discharged to a transition compartment 61, a screen62 is provided to support the catalyst bed. Within the transitioncompartment 61 a steam ring 63 is disposed. The steam ring 63, as shownin FIG. 9 is annularly disposed about the base section 55 of the POxchamber 34. A plurality of interspersed orifices 64 are disposed aboutthe steam ring 63 for discharging steam into the reformate stream. Thesteam ring 63 is preferably triangular in cross section. Advantageously,this configuration permits the ring 63 to share a side with the basesection 55. The exposed side 65 of the ring 63 also advantageouslydeflects the reformate flow outward from the longitudinal axis (x) ofthe reformer 12. The shared side of the triangular steam ring 63facilitates secure attachment to the base section 55 of the POx chamber34. However, a rectangular or square cross section may provide similarresults, and a circular or oval cross section might also be suitable,albeit more difficult to attach without the benefit of a shared side.The steam ring 63 is preferably coupled to a steam delivery tube 66which in turn is attached to a steam source such as a steam generator orsteam separator (not shown).

The inlet assembly 56 of the POx chamber 34 is preferably replaceableand is seated on the base section 55 supporting the cylindrical tube 54of the POx chamber 34 within the reforming chamber 46. Referring to FIG.10, the inlet section 56 is generally a disk-like structure having asubstantially centered opening 67 defined by a cylindrical inner wall 68which aligns with the inner wall of the POx chamber 34 when assembled.The outer circumference of the inlet section 56 in the preferredembodiment is squared on one side and rounded on the opposite side. Abore 69 through the inlet section 56 can be seen in FIG. 10. The bore 69extends from the squared side of the inlet section 56 proximate a cornerthereof and then inward to intersect the cylindrical inner wall 68tangentially. Inserted within the bore 69 is an inlet tube 70. The inlettube is oriented perpendicular to the surface of the squared side. Oneend of the inlet tube 70 may be affixed within the bore 69 and anopposite end is coupled to a mixing manifold 71. This provides a secureattachment of the inlet tube 70 as opposed to prior art delivery tubeswhich may attempt to directly attach to the cylindrical wall of the POxchamber. The exact shaping of the end of the delivery tube is renderedunnecessary since the bore 69 of the present invention is unitary to thereplaceable inlet section. A replaceable, less-expensive,easier-to-construct tangential delivery port to the POx chamber 34 isthus established by this configuration.

As illustrated in FIG. 6, disposed annularly about the reforming chamber46 is the shift reaction zone 72, including two shift reaction beds, theHTS bed 37 and the LTS bed 36. Optionally, a desulfurizing bed catalystmay be added as well. The HTS bed 37, as shown in FIG. 6, spansapproximately one-half the length of the shift reaction zone 72. Aninput side 73 of the HTS bed 37 is disposed adjacent the transitioncompartment 61 for receiving the reformate stream. An outlet side 74 ofthe HTS bed 37 is abutted to an inlet end 36 a of the LTS bed 36 fordischarging shift-reacted constituents from the HTS bed 37. The HTS bed37 is preferably packed with a conventional high-temperature shiftcatalyst, including transition metal oxides, such as ferric oxide(Fe₂O₃) and chromic oxide (Cr₂O₃). Other types of high temperature shiftcatalysts include iron oxide and chromium oxide promoted with copper,iron silicide, supported platinum, supported palladium, and othersupported platinum group metals, singly and in combination. Thesecatalyst may be provided in several of the forms mentioned previously.

According to one aspect of the invention, the HTS catalyst bed isactively cooled. This active cooling is provided to prevent temperaturesfrom rising in the zone to the point of damaging the catalyst. Coolingis advantageously accomplished by heat exchange with reactants flowingthrough tubes placed in the HTS zone. To effect good heat transfer, thecatalyst is preferably in the form of granules, beads, etc., so as topack closely to the heat transfer tubes. However, one or more monolithiccatalyst could also be employed in the HTS zone if appropriatelyconfigured to coexist with a heat exchanger.

The heat transfer tubes are configured through the annular HTS zone asshown in FIG. 6. The helical fuel tube 38 forms a part of fuel line 17.The plurality of coils of the cooling/fuel preheat tube 38 are arrangedco-axially, centered substantially about the longitudinal axis (x) ofthe reformer reactor 12. Heated fuel (or a fuel and steam mixture) iscarried through the HTS bed 37 within the outer helical coils (A) offuel tube 38 and then reaching one end reverses back through the HTS bed37 within the inner helical coils (B) until it arrives at a mixingchamber 76 of the mixing manifold 71.

A secondary preheated fuel line 77 is preferably connected directly tothe mixing manifold 71 for start-up conditions. This direct preheatedfuel feed can be disrupted as soon as the primary fuel source isproperly heated and desulfurized, if necessary.

Also coiled within the HTS bed 37 is the helical oxygen/air tube 40. Theoxygen/air tube 40 is comprised of a plurality of coils beginning with afirst coil attached to oxygen/air inlet 42. The coils are arranged suchthat a first outer set (C) run upward through the HTS bed 37 beforetransitioning into an inner set of coils (D) which run downward throughthe HTS bed 37. Variations of this, as well as other coil arrangements,too numerous to discuss in this disclosure, are certainly possiblewithout departing from the intended scope of the present invention. Theoxygen/air tube 40 and the helical fuel tube 38 converge just prior tothe mixing chamber 76, as shown in FIG. 11, of the mixing manifold 71.The two converged tubes are preferably coaxial as shown. This coaxialconfiguration allows the fluid with the higher flow velocity to assistthe fluid flow of the lower flow velocity. The mixing chamber 76 thendirects the fluids of the converged lines as a homogenous mixture intothe inlet tube 70 toward the POx chamber 34.

The LTS bed 36 begins at its inlet end 36 a proximate the outlet side ofthe HTS bed 37. The LTS bed 36 comprises the remainder of the shiftreaction zone 72. A suitable low-temperature shift catalyst, such asCu/ZnO₂, is packed, preferably as granules, beads, or the like, withinthe LTS bed 36. A helical two-phase water tube 39 is disposed within theLTS bed 36 in a heat transfer relationship (see System and Sub-SystemControl and Operation below) and comprises a plurality of coiledsections. The plurality of coils of the helical water tube 39 arepreferably co-axial with one another about the longitudinal axis (x) ofthe reformer reactor 12. FIG. 6 illustrates a preferred dispersedarrangement of the helical coils of water tube 39 within the LTS bed 36having four columns of coils. Water enters the water tube 39 at inlet 45which itself is connected to a water source 78 (FIG. 24). The flowtravels through the bed within coils (E), then a “U” turn directs theflow into coils (F) moving through the LTS bed 36. The flow thenconnects to coils (G) for a return through the bed 36 before finallyanother “U” turn directs the flow into coils (H) to travel back throughthe bed 36 a final time. The flow is discharged from the reformerreactor 12 through water/steam outlet 79.

Steam is generated by transfer of heat to the water tube 39. Preferablythe tubes 39 are maintained at a sufficient pressure to accommodate atwo-phase water/steam mixture. The two-phase water/steam is eventuallydischarged to a steam separator where it may be separated into liquidand gaseous (steam) portions and made available for use by othercomponents of the system 10.

A screen 80 is positioned at the discharge end of the LTS bed 36. Thescreen 80 provides a barrier for the catalyst while still permittingreformate to flow into the open collection chamber 81 of the reformerreactor 12. A single reformate outlet 82 is positioned at theapproximate center of the reactor top surface 22 providing fluidcommunication with a transfer conduit 20. The transfer conduit 20directs the reformate flow into the PrOx reactor 13.

B. PrOx Reactor:

Referring to the drawings of FIGS. 12-19, a reactor for preferentiallyoxidizing carbon monoxide to carbon dioxide in a hydrogen-rich reformatestream, designated generally as reactor 13, is shown. The reactor 13 isdesigned to direct a radial flow of hydrogen-rich reformate through acatalyst bed. The reactor 13, as shown in FIG. 12, includes an outerbody 83 having protective covering, preferably formed of stainlesssteel. At one end of the body 83 is a reformate inlet 84, and at theother end is a reformate outlet 85. Additionally, a steam/water inlet 86and a steam/water outlet 87 are provided for heat exchange purposes (seeSystem and Sub-System Control and Operation below). Optionally, airinlets (not shown) may be provided to permit reaction air to be diffusedwithin critical areas of the reactor 13. The steam coil allows forsubstantial isothermal PrOx quality.

Within the reactor 13 of the present embodiment, shown in FIG. 13, aflow diffuser 88 is immediately in-line with the reformate inlet 84. Theflow diffuser 88 is comprised of a collection chamber 89 having adischarge end 90 proximate a central manifold 91. The discharge end 90of the flow diffuser 88 has a plurality of apertures for the dischargeof reformate into the central manifold 91. Numerous alternateembodiments of the flow diffuser are possible without departing from theintended scope of the present invention.

The central manifold first zone 91 of the reactor 13 is defined by afirst cylindrical wall 92, preferably of a screen design having multipleopenings disposed about the circumference and length of the wall 92,closed off at one end 93 opposite the flow diffuser 88. Annularlyarranged about the central manifold 91 is a second zone packed with asuitable catalyst in the proper form. The second zone 94, as shown inthe top cross-sectional view of FIG. 14, is also preferably cylindrical,but may be of any shape complementary to the shape of the first zone 91.The second zone 94, in the present embodiment, is packed with a suitablecatalyst—either loosely or tightly—to form a catalyst bed 95. By“suitable” it is meant a catalyst which selectively oxidizes carbonmonoxide to carbon dioxide over diatomic hydrogen, though some oxidationof the hydrogen is inevitably acceptable. The catalyst may be preparedby any of the methods known to those skilled in the relevant art. Whileseveral catalyst exist which may be used with the present reactor 13, acouple of preferred suitable catalyst include Pt/γAl₂O₃ and Au/α-Fe₂O₃.

A second cylindrical wall 96, also preferably of a screen design havingmultiple openings disposed about the circumference and length of thewall 96, defines an outer edge of the catalyst bed 95. The twocylindrical walls, 92 and 96, may also be spherical or hemispherical inshape as alternate embodiments. A helical steam/water or boiler tube 97is arranged within the catalyst bed 95 to substantially traverse the bed95 and provide a heat transfer relationship with the catalyst material.In accordance with this relationship, the packed catalyst preferablymaintains contact with the boiler tube 97. Beginning at a steam/waterinlet 86 the helical tube 97 progresses in a first direction (row A)through the catalyst bed 95 of the second zone 94 and, upon reaching theclosed end 93, retreats in a second opposite direction through thecatalyst bed 95 to the steam outlet 87.

An annular discharge channel 99 is defined between the secondcylindrical wall 96 and an inside surface of the body 83 of the reactor13. The discharge channel 99 opens into a discharge area 100 at an endof the reactor 13 proximate the reformate outlet 85.

In another embodiment of the present invention, the preferentialoxidation of carbon monoxide to carbon dioxide is accomplished in atleast a two stage process. That is, after discharge from the PrOxreactor 13, the hydrogen-rich reformate stream may be further subjectedto a second PrOx reactor 101, as illustrated in FIG. 15. The secondreactor 101 has proven to be an advantageous component in “turn-down.”“Turn-down” refers to the condition whereby the system operates at lessthan the maximum rated power. For instance, a system rated at 50 kWoperating at only 25 kW is in a turn-down condition. While the secondreactor 101 may be designed similar to first reactor 13, in thepreferred embodiment, reactor 101 is adiabatic. This is possible becausethe concentration of carbon monoxide is sufficiently low that oxidationwill not overheat the catalyst bed to promote undesirable reactions (2)and (3) above.

Referring to FIG. 16, one embodiment of the second PrOx 101′ is shown ina side view. The second PrOx 101′ is preferably a cylindrical vesselhaving an inlet 108′, an outer wall 106′, and an outlet 109′. Along thevessel wall is preferably positioned three thermocouple, or other knownsensor devices.

A cross-section of the second reactor 101′, shown in FIG. 17, includes amonolithic catalyst 103 advantageously positioned within a singlereaction zone 104. A distinguishing aspect of the second PrOx reactor101′ over the first PrOx reactor 13 is the absence of cooling coils inthe reaction zone 104′. The incoming reformate stream, with air mixtureas discussed above, encounters the catalyst and begins the oxidation asshown in reaction (1) above. The resulting reformate at discharge has aconcentration of carbon monoxide preferably less than 10 ppm. The secondreactor 101′ typically operates within the temperature range of fromabout 250° F. to about 500° F.

In another alternative preferred embodiment of the PrOx reactor stage ofthe system 10, a chiller condenser 105 may be integrated in-line betweenthe first reactor 13 and the second reactor 101, as shown in FIG. 19.The chiller condenser 105 is preferably a fan used to significantlylower the temperature of the reformate stream after it exits the firstreactor 13. The cooling of the reformate at this point avoidsundesirable side reactions in the reformate, such as the reversewater-gas shift reaction. However, such cooling may also have an adverseaffect on the operation of the PrOx reactor due to an increase in therelative humidity of the stream. These competing interests should beconsidered in the overall integrated system design.

C. Auxiliary Reactor:

The auxiliary reactor 14, as illustrated in FIG. 1, is used incombination with the reformer reactor 12 and the fuel cell 15. A primaryfunction of the preferred auxiliary reactor 14 is to operate as a tailgas combustor burning the anode exhaust gases, comprised mostly ofhydrogen, discharged from the fuel cell 15. However, in conjunction withthe combustion of anode gases, a unique structure of the auxiliaryreactor 12 takes advantage of the excess heat created by the combustionto preheat and desulfurize unreformed fuel and steam for use in otherparts of the hydrogen forming system 10, such as the reformer reactor12.

Referring to FIG. 20, the reactor 14 is preferably a cylindrical vesselhaving a first annular wall 106 defining a first chamber 107. The firstchamber 107 has a diameter (D1), an inlet end 108 and an opposed outletend 109. Disposed within the first chamber 107 is a suitable catalyst110, preferably a platinum (Pt) catalyst in monolith form. The functionof the catalyst 110 within the first chamber 107 is discussed in furtherdetail below.

A second annular wall 111 surrounds the first wall 106 and provides asecond chamber 112 which is annularly disposed about the first chamber107 and has a diameter (D3). The auxiliary reactor 14 further includes athird annular wall 113 disposed between the second annular wall 111 andthe first annular wall 106, the third annular wall 113 extendingsubstantially the length of the second annular chamber 112 andeffectively dividing the second annular chamber 112 into first andsecond annular sub-chambers 114 and 115, respectively. The first annularsub-chamber 114 being disposed between the first chamber 107 and thethird annular wall 113; the second annular sub-chamber being disposedbetween the third annular wall 113 and the second annular wall 112.

As seen in FIG. 20, the third annular wall is of a double-wall 113construction defining third annular chamber 116. Located within thethird annular chamber 116 is fourth annular wall 117, extendingsubstantially the length of the third annular chamber 116 andeffectively dividing the third annular chamber 116 into third and fourthannular sub-chambers, 118 and 119, respectively, the third annularsub-chamber 118 being disposed between the first annular sub-chamber 114and the fourth annular wall 117; the fourth annular sub-chamber 119being disposed between the fourth annular wall 117 and the secondannular sub-chamber 115. The third and fourth annular sub-chambers, 118and 119, respectively, define a U-shaped conduit 120 for the flow ofunreformed fuel, as further explained below.

The reactor 14 additionally includes a flame-type burner assembly 121upstream of the catalyst 110 in the first chamber 107. The burnerassembly 121 is defined by a burner chamber 122, which includes a burnerinlet 123 and a burner outlet 124, the burner outlet 124 beingconnectable to the inlet end 108 of the first chamber 107. The burnerchamber 122 is generally cylindrical and is concentric with the firstannular wall 106 but has a larger diameter (D2) than the diameter (D1)of the first chamber 107. The larger diameter (D2) thus restricts theflow of partially burned, heated gases from the burner chamber 122 intothe first chamber 107. An ignitor 125, preferably a spark plug, isprovided within the burner chamber 122 for creating a spark whichignites a fuel to create a flame at start-up.

The burner assembly 121 is provided in the present embodiment for mixingand burning a heated gas stream within the burner chamber 122. Anauxiliary first fuel, for example natural gas, may be directed to theburner chamber 122 through the burner inlet 123 to form a heated gasstream. The heated gas stream is then further directed to the catalyst110 in the first chamber 107 through the outlet 124. To improvecombustion characteristics during steady-state operation, air in airconduit 127 is preheated by passing between an outer annular shell 126and the second annular wall 111. The inlet end 128 of the air conduit127 is connected to a source of oxygen-containing gas (not shown). Theair conduit 127 directs a stream of oxygen-containing gas to the burnerinlet 123 of the burner assembly 121 for combustion within the burnerchamber 122. The burner inlet 123 is designed to allow for tangentialdelivery of the oxygen-containing gas and the auxiliary first fuel intothe burner chamber 122.

The auxiliary reactor 14 further includes an inlet tube 130 that passesthrough the burner chamber 122 and extends directly into the firstchamber 107. Preferably, the inlet tube 130 is an elongate tube whichextends through the burner chamber 122 for heat exchange with the gasestherein and the fuel cell exhaust gases flowing within the inlet tube130.

Included within the second annular sub-chamber 115 is a helical tube 131that extends the length of the second annular sub-chamber 115. Thehelical tube 131 is configured to allow for the flow of water, asdiscussed in more detail below. The helical tube 131 is connected to thewater/steam line 39 of the reformer 12 (see FIG. 23) via conduit 132 toprovide the water/steam needed for the LTS bed 36 of the reformer 12.Where a more compact reactor design is required, a plurality of fins133, preferably comprised of copper, are spaced in predefined intervalsthroughout the length of the helical tube 131. The fins 133 radiallyextend from the circumference of the helical tube 131 to enhance theexchange of heat between the heated exhaust gas stream and the waterwithin the helical tube 131.

A second preferred embodiment of the auxiliary reactor, as shown in FIG.21, is used preferably for reformers designed to reform a liquidhydrocarbon fuel, such as gasoline or ethanol, as opposed to natural gasor propane. The reactor 200 is preferably a cylindrical vessel having afirst annular wall 206 defining a first chamber 207. The first chamber207 has a diameter (D1), an inlet end 208 and an opposed outlet end 209.Disposed within the first chamber 207 is a catalyst 210, preferably aplatinum (Pt) catalyst in monolith form, for burning fuel cell exhaustto create a heated auxiliary reactor gas stream. The catalyst 210 withinthe first chamber 207 is discussed in further detail below.

A second annular outer wall 211 surrounds the first wall 206 andprovides a second annular chamber 212 having a diameter (D2). Locatedwithin the second annular chamber 212 is a first helical coil 231extending approximately the length of the second annular chamber 212.Additionally, a second helical coil 232 is located within the firstannular chamber upstream of the platinum (PT) catalyst monolith 210.Both the first and second helical coils 231 and 232 are adapted to allowfor the flow of a two-phase water/steam mixture therethrough.

The reactor 200 additionally includes a flame-type burner assembly 221upstream of the catalyst 210 in the first chamber 207. The burnerassembly 221 is defined by a burner chamber 222 at one end of the firstchamber 207. Fuel and air are supplied to the burner chamber 222 viaburner inlet 223 and air conduit 227, respectively. An ignitor 225,preferably a spark plug, is provided within the burner chamber 222 forcreating a spark to ignite the fuel and create a flame at start-up.

The burner assembly 221 is designed for mixing and burning a heated gasstream within the burner chamber 222. An auxiliary first fuel, in thisinstance gasoline, may be directed to the burner chamber 222 throughinlet 223 to form a heated gas stream and the heated gas stream is thenfurther directed to the catalyst 210 in the first chamber 207. The inletend 228 of the air conduit 227 is connected to a source ofoxygen-containing gas 129 (see FIG. 1). The air conduit 227 directs astream of oxygen-containing gas to the burner inlet 223 of the burnerassembly 221 for combustion within the burner chamber 222. The burnerinlet 223 is designed to allow for tangential delivery of theoxygen-containing gas and the auxiliary first fuel into the burnerchamber 222.

The auxiliary reactor 200 further includes an inlet tube 230 that passesthrough the burner chamber 222 and extends to the exit of the burner222. Preferably, the inlet tube 230 is an elongate tube which extendsthrough the burner chamber 222 for heat exchange between the gasestherein and the fuel cell exhaust gases flowing within the inlet tube230.

A third preferred embodiment of the auxiliary reactor, as shown in FIG.22, is used mainly for reformers designed to reform, for instance,natural gas. The reactor 300 is preferably a cylindrical vessel having afirst annular wall 306 defining a first chamber 307. The first chamber307 has a diameter (D1), an inlet end 308 and an opposed outlet end 309.A reaction zone 310 is provided within the first chamber 307.

A second annular outer wall 311 surrounds the first wall 306 andprovides a second annular chamber 312 having a diameter (D2). Locatedwithin the second annular chamber 312 is a helical coil 331 extendingapproximately the length of the second annular chamber 312. The helicalcoil 331 is adapted to allow for the flow of a two-phase water/steammixture therethrough.

The reactor 300 additionally includes a flame-type burner assembly 321upstream of the reaction zone in the first chamber 307. The burnerassembly 321 is defined by a burner chamber 322 at one end of the firstchamber 307. Fuel and air are supplied to the burner chamber 5322 viaburner inlet 323 and air conduit 327, respectively. An ignitor 325,preferably a spark plug, is provided within the burner chamber 322 forcreating a spark to ignite the fuel and create a flame under start-upconditions.

The burner assembly 321 is designed for mixing and burning a heated gasstream within the burner chamber 322. An auxiliary first fuel, naturalgas, is directed to the burner chamber 322 through inlet 323 to form aheated gas stream and the heated gas stream is then further directed tothe reaction chamber 310 in first chamber 307. The inlet end 328 of theair conduit 327 is connected to a source of oxygen-containing gas 129(see FIG. 1). The air conduit 327 directs a stream of oxygen-containinggas to the burner inlet 323 of the burner assembly 321 for combustionwithin the burner chamber 322. The burner inlet 323 is designed to allowfor tangential delivery of the oxygen-containing gas and the auxiliaryfirst fuel into the burner chamber 322.

The auxiliary reactor 300 further includes an inlet tube 330 thatextends directly into the first chamber 307. Preferably, the inlet tube330 is an elongate tube which extends through the burner chamber 322 forheat exchange between the gases therein and the fuel cell exhaust gasesflowing within the inlet tube 330.

II. System and Sub-System Control and Operation

While some of the system controls and operations have been alluded to inthe preceding disclosure, this section of the disclosure is specificallydirected to explaining the preferred operation and means for suchcontrol. The control hardware for each subsystem, i.e., the reformer 12,the PrOx reactor 13, and the auxiliary reactor 14, is discussed,including start-up, steady state, and transient conditions.Modifications to the specific controls may be necessary based upon thecharacteristics of the actual hydrogen forming system and its operation.

A. Water/Steam Loop

With reference to FIG. 23, the important water/steam cooling loop can bemore readily understood. A reservoir (R) supplies water to the system 10through a pump (P). The water is heated at heater (H) to producetwo-phase water/steam mixture at point “A”. The pressure at point “A” ofthe loop is preferably maintained at about 150 psi with an initialtemperature of about 100° C.

The loop runs through a heat exchange section (HE) of the fuelprocessing assembly to provide cooled exhaust gases. A second pass ismade through the anode gas bum section (AB) of the FPA in order to bringthe temperature of the water/steam mixture to about 185° C. at point “B”in steady state operation. The loop is then routed to the fuel reformer12.

The water/steam mixture enters a low temperature shift catalyst bed 36of the fuel reformer 12 first. Heat exchange with the catalyst iscarried out as previously discussed to control the temperature of thebed. Optionally, the loop may pass through the desulfurizing bed (DS)between passes through the LTS bed 36, as shown in FIG. 23.

Leaving the LTS bed 36 the water/steam mixture at point “C” is usuallyabout 185° C. and about 100-150 psi. The loop enters a first PrOxreactor 13 as an active cooling means for the catalyst bed 102. Exitingthe PrOx reactor 13 the water/steam mixture is preferably maintained at185° C. at point “D.” The water/steam mixture enters a steam separator(SS) before returning water to the water reservoir (R) and steam toreformer 12.

Alternatively, the FPA and PrOx steam loop positions may be switched,depending on which bed is more important to heat quickly duringstart-up. Generally, the FPA is first, as shown in FIG. 23.

B. Control Points

FIG. 24 illustrates various control points for an exemplary embodimentof the present invention (double prime notation is used for each of thediscussed points). Additionally, the system pressure is also used toco-regulate several of the disclosed processes, such as the water/steamloop.

A fuel valve 1″ is used for the primary fuel control. The fuel valve 1″allows control of the fuel rate as one means of providing hydrogen ondemand. A water/steam valve 2″ and an air valve 3″ are used at thereformer 12 to control the ratios of steam, air, and fuel. This helps tomaintain the reformer chamber temperature for proper reformation. It ispossible to provide two inlet streams (e.g., air/fuel to the POxchamber, or water/fuel to the steam reformer chamber) if necessary.

A steam control 4″ is used to provide enough steam to complete the watergas shift, as previously discussed. Another air valve 5″ is positionedprior to the inlet of the first PrOx reactor 13. This valve 5″ providescontrol over the theoretical/calculated air delivered to oxidize carbonmonoxide in the reformate stream to carbon dioxide. A third air valve 6″is positioned prior to the inlet of the second PrOx reactor 101′. Aswill be further explained, regulation of air at this point providesadditional air to the PrOx chamber to complete the oxidation of carbonmonoxide during such conditions as start-up, shut-down, and transients.

A routing valve 7″ is used to divert reformate having an excess ofcarbon monoxide to the auxiliary reactor 14 where it can be burned off.This is typical at start-up. As soon as the carbon monoxideconcentration reaches acceptable levels the reformate can be routed bythe valve 7″ to the fuel cell 15. Another start-up control point iscontrol 8″. Control 8″ is used to provide a secondary fuel to the systemon initial warm-up, usually with excess air as well. The secondary fuelis run through the auxiliary reactor 14 before routing to the reformer12.

The final control point is valve 9″ which is used to route a portion ofthe cathode exhaust to the auxiliary reactor. The remaining portion ofthe cathode exhaust is fed to an exhaust outlet or conduit.

Each of the disclosed control points is operated by a central processingsystem (not shown). The system operates via a program capable ofadjusting the operating parameters of the fuel cell system throughperiodic or continuous feedback data from sensors mechanisms or thelike. The data is processed and the system operates the appropriatecontrol point in response to the rapidly changing conditions experiencedduring and transitioning through start-up, steady-state, transients, andshut-down.

C. Fuel Preheat

Referring to FIG. 26, at start-up, or under conditions similar tostart-up conditions, all components of the present system 10 aregenerally “cold,” including the water and fuel sources. The term “cold”is intended not to refer to a specific temperature or range oftemperatures at which the components may operate, but rather to indicatea threshold temperature at which the components operate at an acceptablelevel with respect to efficiency. Naturally, the temperature for eachcomponent will vary widely, and the temperature for any one componentmay vary widely from application to application.

With respect to liquid fuels it is necessary to vaporize the fuel sothat it will burn in the POx chamber 34. This task is preferablyperformed by the auxiliary reactor 14, or a separate heat source, ifavailable. Additionally, because sulfur can be a poison to reformingsystems, certain fuels require desulfurization before entering the POxchamber 34, as well. The auxiliary reactor can be provided with adesulfurizing bed (as described above) to perform this function. To theextent these functions can be accomplished by other integrated systemcomponents after start-up (i.e., when they have achieved a sufficienttemperature), the auxiliary reactor 14 may be discontinue operation inthis manner at that time.

D. Reformer

As illustrated by FIG. 26 and detailed in FIG. 6, preheated fuel (or afuel/steam mixture) enters the reformer reactor 12 at start-up viasecondary fuel inlet 77 connected directly to the mixing chamber 76 ofthe mixing manifold 71. Within the mixing chamber 76 the heated fuel ismixed with a supply of oxygen delivered to the mixing chamber 76 via thehelical oxygen/air tube 40. The homogeneous mixture is directedtangentially, via the inlet tube 70 and the bore 69 of the inlet section56, into the POx chamber 34. The tangential delivery directs thehydrocarbon fuel flow immediately along the inside of the cylindricalwall 54 to effect a rising helical flow within the POx chamber 34.

At start-up a conventional ignition device 135, such as a spark plug,located within the hollow of base section 55, is provided to ignite thefuel/steam/oxygen mixture within the POx chamber 34. The POx chamber 34may or may not contain a reforming catalyst. If used, the POx catalystfor the present invention may be any known catalyst used by thoseskilled in the art, but is preferably either a zirconium oxide (ZrO₂)catalyst (See co-pending U.S. patent application Ser. No. 09/562,789,filed May 2, 2000, now U.S. Pat. No. 6,524,550, and hereby incorporatedby reference) supported on a noble metal (e.g., platinum (Pt), palladium(Pd), nickel (Ni)) in monolith form. The hydrocarbon fuel is ignited,and in the case of methane, hydrogen is liberated in the POx chamber 34according to the following overall reactions:

CH₄+½O₂→CO+2H₂  (a)

and

CO+H₂O⇄TCO₂+H₂  (b)

The exothermic reaction (a) is self-sustaining and maintains anoperating temperature range of from about 700° to about 1200° C. for onespecific embodiment of a catalyzed POx chamber, or from about 1200° toabout 1700° C. for one specific embodiment of a non-catalyzed POx. Thegenerated heat preferably radiates by design outward to the steamreforming zone 35.

The reforming stream optimally travels in a helical path through the POxchamber 34 toward the ventilated end 59 of the cylindrical wall 54. Atthe plurality of apertures 60 the partially reformed fuel/oxygen/steammixture travels outward into the steam reforming zone 35. The steamreforming zone 35 is preferably packed with a nickel catalyst which issupported at the discharge end of the zone by a metal screen 62. Withinthe steam reforming catalyst the remaining fuel undergoes the followingsteam reforming reactions to liberate hydrogen:

 CH₄+H₂O→CO+3H₂  (c)

and

CO+H₂O⇄CO₂+H₂  (d)

The steam reforming reaction (c) is endothermic, requiring a great dealof heat energy to form hydrogen. The reaction draws heat through thecylindrical wall 59 of the POx chamber 34 to maintain an operationtemperature of about 700° to about 1000° C. The reformate stream passesthrough the support screen 62 into the transition compartment 61.

Within the transition compartment 61 the reformate travels optimallyradially outward and is provided a supply of steam from steam ring 63.The steam supply here serves two purposes. First, it helps to cool thereformate for the water-gas shift reaction. Higher temperatures favorthe production of water and carbon monoxide (the “reverse shiftreaction”). Second, the water is a necessary component to react with thecarbon monoxide to produce hydrogen and carbon dioxide. Too little wateradded will result in poor performance of the HTS and LTS shift beds.

The reformate/steam mixture moves axially from the transitioncompartment 61 into the first bed of the shift reaction zone 72, the HTSbed 37. The purpose of the HTS bed 37 is to reduce the concentration ofcarbon monoxide in the reformate stream. The temperature of the HTS bed37 increases as the carbon monoxide concentration is reduced. Theactivity of the catalyst increases with the temperature. However, therising temperature is, of course, detrimental to the purpose because, asstated previously, the higher temperature favors the reverse shiftreaction—i.e., production of water and carbon monoxide. To cool thestream, some of the heat produced in the HTS bed 37 is transferred tothe fuel and oxygen/air supply through the helical tubes 38 and 40,respectively. Still, the operating temperature range of the HTS bed 37is from about 550° C. at the inlet end to about 350° C. at the dischargeend. The concentration of carbon monoxide within the reformate stream isreduced in the HTS bed 37 to about 2.0%.

Optionally, a desulfurizing bed (not shown) may be disposed adjacent theHTS bed 37. The desulfurizing bed would be comprised of a suitablecatalyst such as zinc oxide (ZnO₂) in granule or bead form. As thereformate passes through and contacts the zinc catalyst poisoning sulfurand sulfur compounds would be removed from the stream.

A second shift bed is also provided in the present invention. The LTSbed 36, similar to the HTS bed 37, provides further reduction of thecarbon monoxide concentration in the reformate stream. However, the LTSbed 36 is continuously cooled to provide an isothermal bed. In thepresent embodiment, the LTS bed 36 includes four rows of helicalwindings (E, F, G, and H) of the water tube 39 in a heat exchangerelationship with the bed catalyst. The windings may be reversed ifdesired—i.e., the water inlet feeding winding (H) and finally endingwith the discharge of steam at the outlet of winding (E). The dischargedsteam is preferably directed to a steam separator as discussedpreviously. The cooled shift bed permits greater reduction of the carbonmonoxide concentration in the reformate stream.

The reformate exits the LTS bed 36 through a screen 80 before enteringinto the open discharging chamber 81 of the reformer reactor 12. Thereformate collecting in the discharging chamber 81 is eventuallydirected to an outlet 82 positioned at the approximate center of thereactor top surface 22. From the outlet a transfer conduit 20 directsthe reformate flow into the PrOx reactor 13.

With respect to process controls, four major flows into the reformer 12need to be properly controlled: air, fuel, POx steam and the HTS bedsteam through steam ring 63. The air flow may be controlled using an airflow sensor that feeds back to a valve 136, as illustrated in FIG. 25.Fuel may be controlled using a fuel injector with or without aconventional fuel sensor (not shown). If the fuel flow is choked acrossthe injector and the supply pressure is constant, the flow should beconstant for a given duty cycle, regardless of variations in downstreampressure. Alternatively, differential pressure across the injector maybe controlled to maintain a constant flow for a given duty cycle.Periodic calibration may be necessary to eliminate the need for a fuelsensor. The POx steam flow may be controlled using a motor actuated orsolenoid valve 140, as illustrated in FIG. 28, and an orifice plate 139can be used to measure the steam flow. Control of the HTS bed steam mayalso be accomplished with a pressure actuated or control valve 155 tocontrol the flow rate and the pressure in the system. The pressuresetpoint on the regulator 155 is typically changed manually, or may becontrolled remotely. For transient steam control (see System andSub-System Control and Operation below) to the HTS bed 37 it may bedesirable to vary the pressure setpoint to protect the overallsteam-to-carbon ratio from a drastic drop. Creating such a variablepressure setpoint using a control valve that has feedback from apressure transducer is one alternative.

In addition to the flow controls discussed, several pressure transducersand numerous thermocouples may be necessary to monitor and control thepressure and temperature of the reformer 12.

E. PrOx Reactor

Beginning with the PrOx inlet 13, it is typically connected downstreamof the reformer reactor 12 (as shown in FIG. 1) where a hydrocarbonmaterial is reformed with steam to produce a hydrogen-rich reformatehaving a small, but undesirable, concentration of carbon monoxide(typically <1%). In addition to hydrogen and carbon monoxide, thereformate includes carbon dioxide, water, and other carbon containingcompounds (typically only a few percent or less).

As the reformate enters the reactor 13 at the inlet 84, referring toFIG. 13, it is directed into the central manifold first zone 91 througha diffuser 88. Optionally, the diffuser 88 may be eliminated from thereactor.

In operation, the reformate stream is initially delivered to the inletat a first pressure (P₁) and temperature (T₁), but immediatelyexperiences a pressure drop (ΔP) to a second pressure (P₂) upon enteringthe first zone 91 through the diffuser 88. The temperature of thereformate at this point is initially unaffected. However, the pressureis sufficient to force the reformate stream through the first wall 92 ofthe first zone 91, which has a temperature typically within the range offrom about 200° F. to about 500° F. As the reformate travels radiallyfrom the first zone 91 in a plurality of flow paths it enters thecatalyst bed 95 of the second zone 94 within the reactor 13 adjacent thefirst zone 91.

As the reformate stream encounters the catalyst bed 95, continuing inthe same general diverging directions through the second zone 94, thecarbon monoxide of the stream is oxidized to carbon dioxide by thefollowing reaction:

 CO+½O_(2→CO) ₂

The oxygen necessary for sufficient oxidation to occur may be providedas a mixture with the incoming reformate or introduced to the reactor 13via an incoming air line 141, as shown in FIG. 15. Additionally, as itbecomes necessary to replenish the oxygen for reaction with the carbonmonoxide, secondary air inlets may be provided to direct the desiredquantity of air into the reactor 13. These inlets would help to ensurethat the reformate throughout the catalyst bed 95 has a sufficientsupply of oxygen.

As the secondary air enters the second zone 94, it naturally diffusesthroughout the catalyst bed 95 where it reacts with carbon monoxideadsorbed by the selective catalyst according to the reaction above.

The oxidation of carbon monoxide is further promoted by maintaining thetemperature of the catalyst bed within a desired range, preferably about20° C. to about 170° C. Higher temperatures result in faster reactionrates, permitting the use of a smaller volume reactor, but alsopromoting the undesired side reactions (2) and (3) above. The presentreactor 13 is preferably isothermal.

The PrOx reactor 13 of the preferred system comprises a means foractively cooling the catalyst within the second zone 94. A preferredmeans is shown in FIG. 13. Water/steam tube 97, double-helicallyconfigured throughout the catalyst bed 95, provides a continuous heatexchange with the catalyst bed 95. That is, a flow of water from aconvenient source is pumped continuously into the tube 97 through thewater inlet 86 of the PrOx reactor 13. The cooling fluid flows throughthe water/steam tube 97 drawing heat from the catalyst bed 95, which isin contact with the water/steam tube 97, and discharging from thereactor 13 at the water outlet 87. The water/steam tube 97 is preferablymade from a very good conductive, but non-reactive metal, such as 304SS, to further assist in the heat exchange. It should be understood thatseveral other boiler tube arrangements would be suitable for activelycooling the catalyst bed including, but not limited to, single-helical,longitudinal, and any other configuration which results in the boilertubes being interspersed throughout the second zone 94 or catalyst bed95. It should also be understood that the water/steam tube 97 may beextended into the first zone 91 to actively cool the reformate before itenters the second zone 94.

The discharging heated water/steam from the water outlet 87 of theactive cooling means may be used elsewhere in the system 10. Forinstance, additional tubing may connect the water outlet 87 to a heatexchanger used in a shift reaction zone 72 (see FIG. 6). In such a use,the heat from the heated water/steam may be dissipated within the shiftreaction zone 72 to help raise and maintain the temperature of thereactor 12 to within a desired high temperature range.

In any event, after the reformate stream has passed through the secondzone 94 it enters a discharge flow passing through a second metal(stainless steel) screen wall 96 which defines the outer extent of thesecond zone 94. Referring again to FIG. 13, the reformate then enters anannular discharge channel 99 where it is directed toward the reformateoutlet 85. The concentration of carbon monoxide in the reformate streamat this time should be no more than about 500 ppm. Preferably it islower, for the composition of the reformate, however, also includeshydrogen, carbon dioxide, water, and nitrogen.

The system configuration, in order to deal with flow variations of thereformate made in response to changing power requirements, may include aPrOx reactor 13 (including a second PrOx reactor 13′, as shown in FIG.12) having dynamic control of the oxygen used to oxidize the carbonmonoxide concentration. As discussed previously, the oxygen to carbonmonoxide ratio must be maintained within a stochiometrically balancedrange based on reaction (1) above. Preferably between about 1:4 to about1:1, but most preferably about 1:2, oxygen to carbon monoxide.

To maintain the proper mix ratio, the reactors may include means fordetermining the relative amount of carbon monoxide in the stream. Themeans can be provided by an infrared carbon monoxide sensor 142. Thecarbon monoxide sensor 142, as shown in FIG. 19, may be placed in-lineafter a chiller condenser 105. This position is preferable because: (1)water in the reformate stream may interfere with the infrared sensor;(2) the temperature of the stream has been cooled at this point by thechiller condenser and is, therefore, more suitable for the placement ofthe sensor; and (3) the carbon monoxide concentration is not too low,which makes a good quality signal to noise ratio a better possibility.

The sensor 142, if used, could be read periodically to determine thecarbon monoxide concentration exiting the PrOx reactor 13. A controlscheme can be utilized to control a means for adding an amount of oxygento the reformate stream to produce the desired ratio of oxygen to carbonmonoxide as it enters the PrOx reactor 13, or alternatively, as itenters the second PrOx reactor 13′.

Additionally, the sensor 142 allows for the utilization of means forautomatically adjusting the amount of oxygen containing gas being addedto the stream based upon carbon monoxide concentration fluctuations.

Alternatively, instead of (or in addition to) monitoring theconcentration of carbon monoxide directly, means for determining theconcentration may be indirect. For instance, means may be provided formonitoring at least a first parameter which may give an indication ofthe relative concentration of carbon monoxide. This includes calculatingthe desired amount of oxygen based upon normally expected amounts ofcarbon monoxide to be produced by the source and adjusting oxygen flowbased on these calculated expectations. Possible methods for determiningcarbon monoxide concentrations include determining a change in pressurewithin the preferentially oxidizing reactor or reformer reactor,determining a change in temperature within the preferentially oxidizingreactor or reformer reactor, and measuring time from an event known tocause carbon monoxide fluctuation.

Another alternative embodiment of the present system handles thefluctuating demand in different manner. Such an embodiment, as shown inFIG. 18, includes a PrOx reactor 13″ having a first catalyst bed 95 ahaving a catalyst for oxidation of carbon monoxide in preference todiatomic hydrogen, and a second catalyst bed 95 b having a catalyst foroxidation of carbon monoxide in preference to diatomic hydrogen. Duringoperation, a first manifold 91″ within the reformate conduit 20″connects both the first and second catalyst beds, 95 a and 95 b, inparallel to the reformate source (i.e., the reactor 12) for optionallydirecting the flow through one or the other of the first or second beds,95 a or 95 b, or both in the case of an increase in the reformate sourceflow so as to accommodate the added flow.

Preferably, the dynamic reformate flow is detected by means formonitoring flow of the reformate from the source, such as a suitablypositioned flow meter. The manifold is then designed to be responsive tothe means for monitoring so as to direct the flow of reformate througheither one or both of the catalyst beds in response to a fluctuation ofreformate flow.

A signal is emanated from the flow meter in connection with the sourceand indicating a change in operational parameters of the source whichwill cause a corresponding change in flow of the reformate from thesource. The operational parameters of interest may include increaseddemand, decreased demand, acceleration, deceleration, start-up, shutdown, change of fuels, thermal fluctuations of the source, fuel input,steam input, and the like.

With respect to either a single or double-stage PrOx, the reformate asit exits either PrOx reactor stage of the system, if suitable, may bedirected to the PEM-fuel cell 15, as illustrated in FIG. 2, for use inthe generation of electricity, as is known in the art. Alternatively,where the reformate is not yet suitable for use in a fuel cell, thestream may be either further “cleaned” of compounds which may affect theoperation of the fuel cell or, in the case of reformate formed at startup, it may be combusted in an auxiliary reactor until the quality of theproduct stream reaches acceptable levels.

Combustion is permitted, referring again to FIG. 2, by a discharge line143 connecting the PrOx reactor 13 to the PEM-fuel cell 15, but alsohaving a branched conduit 144 controlled by a valve 145 and connected tothe auxiliary reactor 14. At start up, the valve 145 directs the productstream from the PrOx reactor 13 into the conduit 144 for eventualdischarge into the auxiliary reactor 14 where it can be completelyburned off. Burning off oxidized reformate immediately after start upminimizes poisoning of the PEM-fuel cell 15. This process is usedbecause at start up the steam reforming chamber 35 and the shift beds,36 and 37, of the reformer 12 and the catalyst bed 95 of the PrOxreactor 13 have not achieved the necessary temperatures to reform,shift, or oxidize the hydrocarbon/reformate stream completely. Theresult is a reformate having a high concentration of carbon monoxide orother fuel cell poisons.

The preferred PrOx has two air flows, a water flow, and a fan that mustbe controlled for proper operation. The air flow control is preferably aclosed-loop system which measures the air flow rate using a mass airflow sensor and controls the flow using a proportional solenoid valve(FIG. 24).

The temperature of the PrOx reactor catalyst bed 95 may be controlled bya conventional pool boiler design, known by those skilled in the art.The water level in the pool boiler can be maintained by measuring thewater column height with a differential pressure transducer andcontrolling water flow with a solenoid valve. The steam produced in thePrOx should preferably go to the HTS bed 37, if possible.

The inlet temperature of a second PrOx reactor 101 (see FIG. 15) can becontrolled by varying the air flow over a cross flow heat exchanger 147(FIG. 19). The temperature can be measured with a thermocouple locatedin the reformate line just before the second PrOx reactor 101, asdiscussed above. The air flow can be provided by at least one fan, andpreferably two fans, with a conventional speed control PWM drive (notshown).

F. Auxiliary Reactor

In operation of the first preferred embodiment of FIG. 20, exhaust anodegases from the fuel cell 15 are directed into the inlet tube 130,preheated within the burner chamber 122 of the burner assembly 121 anddirected into the first chamber 107 upstream of the catalyst 110 wherethe gases mix with air.

As the fuel cell exhaust gases pass through the first chamber, thecombination of the heated fuel stream and the platinum (Pt) catalyst 110causes catalytic oxidation of the exhaust gases. The remaining exhaustgases are then directed through the outlet end 109 of the first chamber107 and into the second annular chamber 112, referring to FIG. 20. Thedesign of second annular chamber 112 directs the stream of burnedexhaust gases downwardly through the first annular sub-chamber 114, incounter-flow fashion to the direction of the flow of the exhaust gasesin the first chamber 107. At the end of the first annular sub-chamber114, the stream is redirected upwardly through the second annularsub-chamber 115 in counter-flow fashion with the direction of the flowof gases within the first annular sub-chamber 114. Located at theopposed end of the second annular sub-chamber 115 is an exhaust outlet152, which allows the remaining exhaust gases to be released into theatmosphere.

Included within the second annular sub-chamber 115 is a helical tube 131that extends the length of the second annular sub-chamber 115. Thehelical tube 131 is configured to allow for the flow of water. The fuelcell exhaust stream flowing upwardly through the second annularsub-chamber 115 exchanges heat with the water found within the helicaltube to assist in the formation of a two-phase water/steam mixture. Thehelical tube 131 is connected to the water/steam line 39 (FIGS. 2 and23) of the reformer 12 via the conduit 132 to provide the water/steamneeded for the LTS bed 36 of the reformer 12 (FIG. 6). Where a morecompact reactor designed is required, a plurality of fins 133,preferably comprised of copper, are spaced in predefined intervalsthroughout the length of the helical coil 131. The fins 133 radiallyextend from the circumference of the helical coil to enhance theexchange of heat between the heated exhaust gas stream and the waterwithin the helical coil 131.

Located at the end of the reactor 14 opposite the burner assembly 121 isunreformed fuel inlet 108, which allows for the introduction ofunreformed fuel into the reactor 14. The unreformed fuel is directedthrough U-shaped conduit 120, defined within the third annular wall 113,in constant heat exchange relationship with the stream of fuel cellexhaust gases though the first and second annular sub-chambers, 114 and115, respectively. The flow of the unreformed fuel through the firsthalf of the U-shaped conduit 120, i.e., the third annular sub-chamber118, parallels the flow of the fuel cell exhaust gas through the firstannular sub-chamber 114, and the flow of the unreformed fuel through thesecond half of the U-shaped conduit 120, i.e, the fourth annularsub-chamber 119, parallels the flow of the fuel cell exhaust gasesthrough the second annular sub-chamber 115. The resultant exchange ofheat from the exhaust gases to the unreformed fuel preheats theunreformed fuel for introduction into the reformer 12 via fuel line 17.Preferably, a zinc-containing catalyst is placed within either of bothhalves of the U-shaped conduit 120, i.e., the third annular sub-chamber118 or the fourth annular sub-chamber 119, for desulfurizing theunreformed hydrocarbon fuel flowing therethrough.

The auxiliary reactor 14 is used to combust exhaust from the PrOx notconsumed in the fuel cell 15. This allows the emissions to be maintainedat near zero. The excess heat is used to generate steam. The overallgoal of the control strategy, therefore, is to keep the catalyst 110 ata temperature high enough to burn the combustibles in the anode exhaust,maximize steam production, and keep emissions low. To accomplish this itis necessary to ensure that the auxiliary reactor 14 is operating leanand at a temperature range of about 1000° F. (approx. 550° C.) to about1470° F. (approx. 800° C.). One method of doing this is to set a desiredtemperature and excess oxygen level for the auxiliary reactor 14. Theoxidant flow rate can be adjusted based on the temperature in thecatalyst 110 to maintain the desired temperature. As changes are made inthe system operation, an oxygen sensor 148 will detect these changes andalso adjust the oxidant flow rate to ensure lean operation.

In operation of the second preferred embodiment, as seen in FIG. 21,exhaust anode gases from the fuel cell 15 are directed into the inlettube 230, preheated within the burner chamber 222 and directed into thefirst chamber 207 upstream of the platinum (Pt) catalyst 210. As thefuel cell exhaust gases pass through the first chamber 207, thecombination of the heated fuel stream and the platinum (Pt) catalyst 210causes catalytic oxidation of the exhaust gases. The remaining exhaustgases are then directed through the outlet end 209 of the first chamber207 and into the second annular chamber 212, as shown in FIG. 21. Thedesign of second annular chamber 212 redirects the stream of burnedexhaust gases upwardly in counterflow fashion to the direction of thestream within the first chamber 207. Located at the opposed end of thesecond annular chamber 212 is an exhaust outlet 252, which allows theremaining exhaust gases to be released into the atmosphere.

The fuel cell exhaust stream flowing upwardly through the second annularchamber 212 exchanges heat with the water/steam found within the firsthelical tube 231 to assist in the formation of a two-phase water/steammixture. The two-phase water/steam mixture in the first helical tube 231is then directed to the second helical coil 232 via conduit 233,external to the reactor 14. The additional heat within the first chamber207 is furthered transferred to the two-phase water/steam mixture withinthe second helical coil 232 to further promote the formation of steam.The second helical tube 232 is connected to the water/steam line 39(FIG. 23) of the reformer 12 to provide the steam needed for the LTS bed36 (FIG. 6).

The third preferred embodiment, as seen in FIG. 22, directs exhaustanode gases from the fuel cell 15 into the inlet tube 330, preheats theanode exhaust gases within the burner chamber 322 and directs theexhaust gases into the first chamber 307 upstream of the platinum (Pt)catalyst 310. As the fuel cell exhaust gases pass through the firstchamber, the combination of the heated fuel stream and the platinum (Pt)catalyst 310 causes catalytic oxidation of the exhaust gases. Theremaining exhaust gases are then directed through the outlet end 309 ofthe first chamber 307 and into the second annular chamber 312, as shownin FIG. 22. The design of second annular chamber 312 redirects thestream of burned exhaust gases upwardly in counterflow fashion to thedirection of the stream within the first chamber 307. Located at theopposite end of the second annular chamber is an exhaust outlet 352,which allows the remaining exhaust gases to be released into theatmosphere.

The fuel cell exhaust stream flowing upwardly through the second annularchamber 312 exchanges heat with the water/steam found within helicaltube 331 to assist in the formation of a two-phase water/steam mixture.Helical tube 331 is connected to the water/steam line 39 (FIG. 23) ofthe reformer 12 to provide the steam needed for the LTS bed 36 (FIG. 6).

G. Steady-State Control

Control of the system 10 becomes easier once start-up is complete andthe fuel cell 15 is brought on-line. A description of the control foreach subsystem during steady-state operation is given below withparticular reference to FIG. 27. At all times during operation, thevalues of critical process variables should be checked against upper andlower limits. If any value is out of these limits, an alarm can betriggered to notify the operator.

1. Reformer

Once the reformer 12 has been brought up to the preferred operationtemperature, it is controlled by maintaining the desired power,equivalence ratio, and steam to carbon ratio in both the POx chamber 34and the HTS bed 37. The temperature should be held at the desiredsetpoint by slightly adjusting the air flow and thus the equivalenceratio. To adjust the steam reformer exit temperature, the POx chambertemperature setpoint can be adjusted. The POx steam to carbon ismaintained using the control valve 155 to control steam flow. The systemis designed to produce the remaining steam needed internally and thisexcess is fed to the HTS bed 37 through a back-pressure regulator 140.

2. PrOx Reactor

The oxygen to carbon monoxide ratio in the first PrOx reactor 13 shouldbe a fixed number determined empirically from initial testing doneconventionally to characterize the system 10. Provided there issufficient air, the design of the first PrOx reactor 13 should be suchthat the carbon monoxide output will be relatively constant with varyingcarbon monoxide at the reformate inlet 84. In the event that there areno online analyzers for the system 10, the oxygen to carbon monoxideratio can be set to account for an upper limit of steady state inletcarbon monoxide. The oxygen to carbon monoxide ratio for the second PrOxreactor 13′ should be adjusted to maintain a fixed temperature risethrough the catalyst bed 95 and outlet carbon monoxide concentrationsless than 10 ppm.

3. Auxiliary Reactor

The auxiliary reactor 14 is used to burn off anything not consumed inthe fuel cell 15 during steady-state operation. This allows theemissions to be maintained at near zero. The excess heat is used togenerate steam. The overall goal of the control strategy, therefore, isto keep the catalyst at a temperature high enough to burn thecombustibles in the anode exhaust, maximize steam production, and keepemissions low. At the same time, the upper temperature limit on thecatalyst must be avoided. To accomplish this it is necessary to ensurethat the Auxiliary reactor 14 is operating lean and within a temperaturerange of about 1000° to about 1470° F. One method of doing this is toset a desired temperature and equivalence ratio for the Auxiliaryreactor 14. The oxidant flow rate can be adjusted based on thetemperature in the catalyst to maintain the desired temperature. Aschanges are made in the system operation, the oxygen sensor 148 shoulddetect these changes and the air flow rate will then be adjusted toensure lean operation. It may be necessary to vary the equivalence ratiosetpoint if the concentration of hydrogen in the anode exhaust variessignificantly.

4. Water/Steam

At steady state, the pump speed and thus water flow rate are controlledbased on the total steam being generated. In the present embodiment, thesteam added to the POx chamber 34 and the HTS bed 37 are added togetherand multiplied by a factor of safety. This becomes the setpoint for thewater flow rate, and thereby ensures that superheated conditions areavoided. If a superheated condition occurs, the factor of safety isautomatically modified to add additional water until the steamtemperature returns to the saturated temperature. An alternativeapproach determines the necessary water flow according to an operatingmap based on fuel input.

H. Transient Control

During transient conditions, the control of the reforming system 10 mustbe modified slightly to prevent excessive temperatures, high carbonmonoxide concentration, and other emissions. The following disclosurecontains a general description of control goals of each subsystem duringtransient conditions.

1. Steam Generation-Generally

In overview, according to the invention, the system 10 integrateselements of thermal control with elements of necessary steam generation.For example, temperature of shift beds are impacted by heat exchangewith a steam generating system (or steam loop). Also, reformatetemperature is impacted by addition of steam in connection with a hightemperature shift reaction. Steam condensation and water separation fromthe reformate is integrated as cooling of reformate to the benefit ofpreferential oxidation.

Also, according to the invention, steam generation is integrated in aunique way in the system 10, with processes and apparatus responsiblefor dynamic (e.g. transient) operation, such as following load demands,and rapid start-ups. Other advantages and aspects will be disclosedherein with respect to the system's overall thermal balance and dynamicresponse control.

FIG. 28 discloses the system 10 control scheme for dynamic control. Thiscontrol design and process is applicable for the many uses where a loadon the system is dynamic, that is, the demand for hydrogen-rich gasvaries. For example, transportation fuel cell applications will requireacceleration and deceleration of the vehicle, which will cause a dynamicresponse from the system if integrated into such a system. Moreimportantly, the need for a quick response will be required, andaccording to the invention, the disclosed system can meet that need.

Generally, the process includes supplying a hydrocarbon fuel and oxygenat a first rate to reformer reactor 12 for steady state operation. Steamgenerated by the auxiliary reactor 14 and the heat exchange in the lowtemperature shift zone 36 is also supplied to the reactor 12 at a firstrate for steady state performance. At steady state pressure on the steamloop 16 including auxiliary reactor 14, the heat exchange tubes 39 inthe low temperature shift bed 36 and the steam separator 105 is kept ata pressure of about 130 psi. Upon a change in demand, either for more orfor less hydrogen, the system changes the rate of supply of each of thehydrocarbon fuel and the steam to a second supply rate. The change insteam demand causes an immediate change in loop steam pressure.According to the invention, the steam pressure is permitted to changewithin an acceptable range. Various aspects of the system design permitsthis as well as a rather rapid recovery of the loop 16 steam pressure.

Preferably the acceptable range within which the steam pressure ispermitted to change is about 200 psi, but more preferably about 150 psi.In other words, the steam pressure for system 10 is permitted to varybetween about 50 psi to about 200 psi during a transient operation.

For example, if the demand on system 10 increased, a control signalwould be sent from the device, such as a fuel cell, depicted genericallyas a controller (C) in FIG. 28. Based upon that signal, a direct andproportional signal would be sent to air supply valve (AV1) hydrocarbonfuel supply control valve (FV1) to increase the rate of each.

Also in response to the control signal both steam valves (SV1) and (SV2)are respectively adjusted to increase supply of steam to the fuel steammixture and to increase the supply of steam to the reformate before itenters the high temperature shift reaction. According to one aspect ofthe invention, the supply of both of these constituents can be, andpreferably is kept at the steady state steam to carbon ratio of about 3during the transient response.

Due to the fact that the system 10 employs two-phase pressurized steam,the delivery of extra steam from the steam separator 151 occurs withinfractions of a second and can be delivered in a matter of one or moremilliseconds. That is, upon a drop in pressure when valves (AV1) and(FV1) are adjusted to increase supply, the pressure drop causes theimmediate production of steam from latent heat in the water of thetwo-phase mixture. The system response is also significantly aided,according to the invention, by the almost immediate (millisecond)creation of steam from the heat exchangers (HE) in the low temperatureshift and PrOx catalyst beds. Not only is there latent heat in the waterin those heat exchangers, there is a relatively large heat bufferprovided by the catalysts and reactor masses. It is believed that steamfrom these heat exchangers is readied for supply within one or moremilliseconds as well.

In response to the control signal, the valve (AV2) is adjusted toincrease air flow to the auxiliary reactor 14. An oxygen sensor 148senses the that the oxygen concentration is over a set point andtriggers a control response of valve (FV2) to increase the fuel to theauxiliary reactor 14. The result is added steam generation. The oxygensensor 148 will continue to attempt to keep the fuel supply to theauxiliary reactor 14 in limit. In the meantime, as the auxiliary reactor14 and the heat exchangers (HE) in the reformer 12 and the PrOx 13continue to generate steam, the pressure begins to return to the desired130 psi. According to one aspect of the invention, synergistically, thehigher output by the reformer and PrOx increases their contribution tothe generation of steam. Once at the new power or burn rate, the system10 temperatures also tend to better equilibrate due to the advancedamount of steam supply due to the added heat exchange presented by thedesign.

As disclosed in FIG. 28, the response of the air valve (AV2) to thecontrol signal (CS) is indirect. The control signal (CS) is firstassessed and pursuant to predetermined values in a computer memorylookup table (LT), the appropriate auxiliary reactor burn rate isdetermined and a secondary control signal is sent to valve (AV2).However, while the pressure is returning to the desired 130 psi,supplementary trim control signals (TS) are sent to air valve (AV2)according to pressure values sensed by pressure gauge (PG) to adjust theair supply downward. Again, the oxygen sensor 148 will reduce the fuelaccording to the sensed reduction of air.

According to another aspect of the invention, this trimming processoccurs independently of whether or not a control signal is sent from thecontroller (C).

This trimming process helps maintain the system thermal equilibriumcaused by other factors, such as changes in system efficiencies, andambient temperature changes.

It should be noted, that thermal stability of the partial oxidationreaction is controlled by a POX trim signal (TS) generated in responseto sensor (thermocouple) 149. This trim signal causes the air flow tothe POx to be adjusted based upon temperature of reactants in thepartial oxidation reaction. Preferably this trim signal can be generatedindependently of a control signal from controller (C).

Also, according to another aspect of the invention, the sizing of thepartial oxidation zone and downstream steam reforming zone can be suchthat high volumetric flow rates caused by either a very large increasein hydrogen demand or a high steady state demand, will cause a muchhigher mixing velocity and swirling of the gases to extend vigorouslyupward in the POx chamber which raises its efficiency and thermaloutput. At some higher flow levels, partial oxidation at significantlevels will begin to be promoted by the steam reforming catalyst.

It is also useful to consider a decrease in demand to illustrate otheraspects of the invention. Upon a downturn in hydrogen demand, a controlsignal is generated and sent as in the discussion above. All of thevalves and controls respond exactly as above but to decrease air, fueland steam supplied to the various components. The pressure is againpermitted to rise, but preferably not to more than 200 psi in thisembodiment. The system again comes back to equilibrium. However, thechallenge faced with a decrease is what to do with the excess steam, andor thermal energy. The system 10 is designed and sized such that only aportion of the steam is generated by the reformer 12 and PrOx reactor 13which may have significantly higher thermal mass than the auxiliaryreactor and steam loop. In the preferred embodiment of system 10, onlyabout half of the thermal energy needed for steam generation is suppliedby the auxiliary reactor 14. In other embodiments, a different balanceof thermal energy may be desired. Also, the fact that heat exchange isdone with tube boilers coupled with an auxiliary steam generator, bothpermit the total water and steam mass to be smaller, versus for examplea pool boiler. This permits reduction in the amount of excess steamgenerated after turn down. It is also this relatively low ratio ofcatalyst mass to the mass of water in each of: (1) the tube heatexchangers (HE); and, (2) the system as a whole, that permits such arapid response in steam generation in a turn-up scenario.

Another significant transient is start-up. According to one aspect ofthe invention provides that upon start up, the auxiliary reactor 14 isstarted to generate steam. This steam is routed through the catalystbeds 36 and 37 as discussed herein. This advantageously permits thesereactors to address carbon monoxide production earlier after start upthan otherwise would be the case. This permits an earlier delivery of anacceptable hydrogen-rich stream to a load, such as a fuel cell 15.

2. Reformer

During transients, the goal for the reformer 12 is to change power asquickly as possible while maintaining the steam to fuel ratio in the POxchamber 34, as well as the overall steam to fuel ratio and thetemperature in the POx chamber 34. This helps prevent any large spikesin the carbon monoxide concentration. One component of the control ofthe reformer 12 during transient conditions is for the flows of fuel,air, and steam to all follow each other. The time required for the airto reach a new steady-state point will directly affect the speed of thetransients. When a request for a change in air is sent, the entirereformer 12 must wait for this change to occur. As the air flow isramped up or down to the desired flow rate, the fuel flow rate mustfollow this change to maintain the set ratio (preferably, about 1.5steam to carbon in the reformer 12 with another 1.5 added directly tothe HTS bed 37). The steam flow rate to the POx follows the fuel flowrate to maintain the desired steam to carbon ratio. Once the transientcondition is complete, the automatic control to maintain steam to carbonratio in the POx chamber 34 can be resumed.

When increasing the power in the system 10, the steam to carbon ratio inthe HTS bed 37 will most likely drop (since the system will notimmediately increase steam production) unless an adjustment is made inthe steam system. If the overall steam to carbon ratio drops, the carbonmonoxide will increase at the exit of the reformer 12. To prevent this,it may be necessary to drop the pressure setpoint in the steam loop toallow extra steam into the HTS bed 37. This adjustment can help tominimize any spike in carbon monoxide concentration exiting the reformer12 and the extra air required by the PrOx reactor 13 during transientconditions. The pressure should then be gradually increased back to thenominal value as steam production increased at the new power and theoverall steam to carbon ratio begins to rise again. Clearly adjustingthe pressure in the steam loop is not the best solution if the system isgoing through frequent transient conditions. Such potentially couldresult in a loss of steam pressure and a drop in the catalyst bedtemperatures. In this case, it may be necessary to re-light theauxiliary reactor burner chamber 122 and generate additional steam tomaintain the steam loop pressure.

3. PrOx Reactor

If steam control is maintained in the reformer, PrOx air flow duringtransients should adjust to maintain to set oxygen to carbon monoxideratios the reformate flow change. Where a loss of steam flow rate occursand elevated carbon monoxide levels occurs, the oxygen to carbonmonoxide ratio in the first PrOx reactor 13 can be mapped against timeto give an elevated amount of air until the LTS bed exit carbon monoxideconcentration level returns to its steady state value. Such a map can beused to determine empirically where an online analyzer will beavailable. The oxygen to carbon monoxide ratio for the second PrOxreactor 13′ need not be adjusted since the carbon monoxide outlet fromthe first PrOx 13 does not change during the transient.

4. Auxiliary Reactor

Control of the auxiliary reactor 14 during transient conditions issimilar to control during steady state. As more or less anode exhaustreaches the auxiliary reactor 14, the oxygen sensor 148 picks up on thischange and adjust the air flow rate into the system 10. If theconcentration of hydrogen in the anode exhaust changes significantly,the equivalence ratio setpoint for the auxiliary reactor 14 will beadjusted accordingly to maintain the desired temperature.

5. Water/Steam

Since maintaining steam in the fuel processing system is so important tothe performance of the system 10, appropriate adjustments of the waterflow rate into the system 10 are also extremely important. Anincrease/decrease in power will result in more/less steam production andthe water flow rate should be changed accordingly. The steam flow rateinto the POx chamber 34 and HTS bed 37 will lag behind this change,however. Alternatively, it may be necessary to estimate what the waterflow rate should be at different powers experimentally and use thisinformation during transients instead of relying on the total flow rateof steam.

While specific embodiments have been illustrated and described, numerousmodifications are possible without departing from the spirit of theinvention, and the scope of protection is only limited by the scope ofthe accompanying claims.

We claim:
 1. A high-efficiency system for reaction reforming hydrocarbonfuel to generate hydrogen-rich reformate gas for use in an associatedfuel cell, the system comprising: a gas generator having at least oneendothermic reaction zone in thermal contact with at least oneexothermic reaction zone; at least one shift reactor; a preferentialoxidation (PrOx) reactor; an auxiliary reactor for oxidizing reformatecomponents not consumed by the associated fuel cell thereby minimizingexhaust and maximizing extraction of thermal energy; and a heatexchanger in the auxiliary reactor arranged to allow the circulation ofat least fuel and water through the heat exchanger; and a heat exchangerin at least one of the shift reactor and the PrOx reactor arranged tocirculate water so as to utilize the thermal energy generated by anexothermic reaction to preheat input components and heat catalysts. 2.The system of claim 1, wherein a water/steam mixture is circulated as atwo-phase mixture in a first section of circulation through the heatexchange system, wherein the two-phase mixture absorbs heat and activelycools the temperature of at least one of a PrOx reactor and a shiftreaction zone, and optionally of the auxiliary reactor.
 3. The system ofclaim 2, further comprising a water/steam separator for separating thewater from the steam, wherein the steam is passed into heat exchangersin at least one of a high temperature shift reaction zone and a gasgenerator.
 4. The system of claim 1, wherein the gas generator comprisesat least one of a partial oxidation (POx) reactor and a steam reformer.5. The system of claim 1, wherein the gas generator comprises anautothermal reactor having a partial oxidation (POx) zone and a steamreforming zone.
 6. The system of claim 1, further comprising a condenserdownstream of the PrOx reactor to extract water from the hydrogen-richreformate issuing from the PrOx reactor, and a second PrOx reactordownstream of the condenser to oxidize CO in the reformate to CO₂ beforethe reformate enters the fuel cell.
 7. The system of claim 6, whereinthe heat exchange system further comprises means for introducing steaminto the high temperature shift section so as to maintain anapproximately constant pressure at the steam separator, wherein thepressure is selected to place the boiling point of the water at aboutthe desired temperature range in at least one of the low temperatureshift reactor and the first PrOx reactor.
 8. The system of claim 1,further comprising means for controlling temperatures downstream of thehigh temperature shift reaction zone by supplying water at a ratesufficient to maintain a two-phase mixture of water and steam in suchdownstream sections.
 9. The system of claim 1, wherein a bypass valvediverts reformate to the auxiliary reactor from the associated fuelcell, during at least one system condition selected from startup,shutdown, transients in demand, and abnormal levels of temperature orpressure in the system.
 10. The system of claim 1, further comprising anelectronic device for performing a calculation to determine whether acarbon monoxide level in the reformate is below a critical level. 11.The system of claim 1, wherein the shift reactor comprises a first shiftreaction zone and a first heat exchanger, and a shift exchange catalystin the shift reaction zone in thermal contact with the heat exchanger.12. The system of claim 1, in which the auxiliary reactor comprises atleast one reaction zone and at least one heat exchanger.
 13. Ahigh-efficiency system for reaction reforming hydrocarbon fuel togenerate hydrogen-rich reformate gas for use in an associated fuel cell,the system comprising: a reformer reactor which receives inputs ofhydrocarbon fuel, air, and steam; at least one shift reactor operablyconnected to the reformer reactor; a preferential oxidation (PrOx)reactor operably connected to the shift reactor wherein reformate isgenerated from a hydrocarbon fuel by passing said fuel through thereformer, shift, and PrOx reactors, an auxiliary reactor for oxidizingreformate components not consumed by the associated fuel cell and usingheat from oxidizing said reformate components to preheat a hydrocarbonfuel and water; a water circulating system for circulating water andsteam through the auxiliary reactor and through a heat exchangerarranged to exchange heat within at least one of the shift and PrOxreactors and; a control device for regulating the efficient operation ofthe system during transient and steady state operation; and wherein thecontrol device, in response to transient conditions within the system,adjusts the feed rate of fuel to at least one of the reformer andauxiliary reactors.
 14. The high-efficiency system of claim 13 whereinthe water circulating system is arranged to provide a feed stream ofsteam to the reformer reactor.
 15. The high-efficiency system of claim13 wherein the control device generates a control signal which controlsan air supply valve and a hydrocarbon fuel supply valve which supply thereformer reactor.
 16. The high-efficiency system of claim 13 furthercomprising a computer memory lookup table to which the control signal isrouted and which uses the control signal to adjust an air feed rate tothe auxiliary reactor.
 17. The high-efficiency system of claim 13wherein the control device generates a control signal which controls awater flow rate within the water circulating system to the heatexchanger in at least one of the shift and PrOx reactors.
 18. Thehigh-efficiency system of claim 13 wherein the control device is anelectronic device.
 19. A high-efficiency system for reaction reforminghydrocarbon fuel to generate hydrogen-rich reformate gas for use in anassociated fuel cell, the system comprising: a reformer reactor; atleast one shift reactor operably connected to the reformer reactor; apreferential oxidation (PrOx) reactor operably connected to the shiftreactor; an auxiliary reactor for oxidizing reformate components notconsumed by the associated fuel cell; a heat exchanger utilizing a heattransfer medium to absorb heat generated by the oxidation reactionwithin the auxiliary reactor and arranged to use said heat transfermedium to modify an operating temperature within at least one of theshift and PrOx reactors; and, a reformer fuel warming system whichutilizes heat generated by the auxiliary reactor.